* add RunImpersonateAsync overloads

* skip on full framework

* run test netcoreapp only

* skip tests on nanoserver

* address PR feedback

* address PR feedback

* address PR feedback

* address PR feedback

* Update WindowsIdentity.cs

update comment

* Update WindowsIdentity.cs

update comment

* Update WindowsIdentity.cs

Fix comment

* Update WindowsIdentity.cs

fix comment

* Fix comment

configure.ac: remove AC_SEARCH_LIBS for libintl

Same type can be loaded by multiple threads in parallel in rare situations

Fixes #1847

* Update dependencies from https://github.com/dotnet/arcade build 20200115.5

- Microsoft.DotNet.XUnitExtensions - 5.0.0-beta.20065.5
- Microsoft.DotNet.VersionTools.Tasks - 5.0.0-beta.20065.5
- Microsoft.DotNet.ApiCompat - 5.0.0-beta.20065.5
- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20065.5
- Microsoft.DotNet.Build.Tasks.Configuration - 5.0.0-beta.20065.5
- Microsoft.DotNet.Build.Tasks.Feed - 5.0.0-beta.20065.5
- Microsoft.DotNet.Build.Tasks.Packaging - 5.0.0-beta.20065.5
- Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk - 5.0.0-beta.20065.5
- Microsoft.DotNet.CodeAnalysis - 5.0.0-beta.20065.5
- Microsoft.DotNet.GenAPI - 5.0.0-beta.20065.5
- Microsoft.DotNet.GenFacades - 5.0.0-beta.20065.5
- Microsoft.DotNet.Helix.Sdk - 5.0.0-beta.20065.5
- Microsoft.DotNet.RemoteExecutor - 5.0.0-beta.20065.5
- Microsoft.DotNet.XUnitConsoleRunner - 2.5.1-beta.20065.5

* Update dependencies from https://github.com/dotnet/arcade build 20200116.1

- Microsoft.DotNet.XUnitExtensions - 5.0.0-beta.20066.1
- Microsoft.DotNet.VersionTools.Tasks - 5.0.0-beta.20066.1
- Microsoft.DotNet.ApiCompat - 5.0.0-beta.20066.1
- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20066.1
- Microsoft.DotNet.Build.Tasks.Configuration - 5.0.0-beta.20066.1
- Microsoft.DotNet.Build.Tasks.Feed - 5.0.0-beta.20066.1
- Microsoft.DotNet.Build.Tasks.Packaging - 5.0.0-beta.20066.1
- Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk - 5.0.0-beta.20066.1
- Microsoft.DotNet.CodeAnalysis - 5.0.0-beta.20066.1
- Microsoft.DotNet.GenAPI - 5.0.0-beta.20066.1
- Microsoft.DotNet.GenFacades - 5.0.0-beta.20066.1
- Microsoft.DotNet.Helix.Sdk - 5.0.0-beta.20066.1
- Microsoft.DotNet.RemoteExecutor - 5.0.0-beta.20066.1
- Microsoft.DotNet.XUnitConsoleRunner - 2.5.1-beta.20066.1

* Update dependencies from https://github.com/microsoft/vstest build 20200116-01

- Microsoft.NET.Test.Sdk - 16.5.0-preview-20200116-01

* Update dependencies from https://github.com/dotnet/arcade build 20200117.2

- Microsoft.DotNet.XUnitExtensions - 5.0.0-beta.20067.2
- Microsoft.DotNet.VersionTools.Tasks - 5.0.0-beta.20067.2
- Microsoft.DotNet.ApiCompat - 5.0.0-beta.20067.2
- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20067.2
- Microsoft.DotNet.Build.Tasks.Configuration - 5.0.0-beta.20067.2
- Microsoft.DotNet.Build.Tasks.Feed - 5.0.0-beta.20067.2
- Microsoft.DotNet.Build.Tasks.Packaging - 5.0.0-beta.20067.2
- Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk - 5.0.0-beta.20067.2
- Microsoft.DotNet.CodeAnalysis - 5.0.0-beta.20067.2
- Microsoft.DotNet.GenAPI - 5.0.0-beta.20067.2
- Microsoft.DotNet.XUnitConsoleRunner - 2.5.1-beta.20067.2
- Microsoft.DotNet.GenFacades - 5.0.0-beta.20067.2
- Microsoft.DotNet.Helix.Sdk - 5.0.0-beta.20067.2
- Microsoft.DotNet.RemoteExecutor - 5.0.0-beta.20067.2

* Update dependencies from https://github.com/dotnet/arcade build 20200118.1

- Microsoft.DotNet.XUnitExtensions - 5.0.0-beta.20068.1
- Microsoft.DotNet.VersionTools.Tasks - 5.0.0-beta.20068.1
- Microsoft.DotNet.ApiCompat - 5.0.0-beta.20068.1
- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20068.1
- Microsoft.DotNet.Build.Tasks.Configuration - 5.0.0-beta.20068.1
- Microsoft.DotNet.Build.Tasks.Feed - 5.0.0-beta.20068.1
- Microsoft.DotNet.Build.Tasks.Packaging - 5.0.0-beta.20068.1
- Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk - 5.0.0-beta.20068.1
- Microsoft.DotNet.CodeAnalysis - 5.0.0-beta.20068.1
- Microsoft.DotNet.GenAPI - 5.0.0-beta.20068.1
- Microsoft.DotNet.XUnitConsoleRunner - 2.5.1-beta.20068.1
- Microsoft.DotNet.GenFacades - 5.0.0-beta.20068.1
- Microsoft.DotNet.Helix.Sdk - 5.0.0-beta.20068.1
- Microsoft.DotNet.RemoteExecutor - 5.0.0-beta.20068.1

* Update dependencies from https://github.com/microsoft/vstest build 20200120-01

- Microsoft.NET.Test.Sdk - 16.5.0-preview-20200120-01

* Update dependencies from https://github.com/dotnet/arcade build 20200121.3

- Microsoft.DotNet.XUnitExtensions - 5.0.0-beta.20071.3
- Microsoft.DotNet.VersionTools.Tasks - 5.0.0-beta.20071.3
- Microsoft.DotNet.ApiCompat - 5.0.0-beta.20071.3
- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20071.3
- Microsoft.DotNet.Build.Tasks.Configuration - 5.0.0-beta.20071.3
- Microsoft.DotNet.Build.Tasks.Feed - 5.0.0-beta.20071.3
- Microsoft.DotNet.Build.Tasks.Packaging - 5.0.0-beta.20071.3
- Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk - 5.0.0-beta.20071.3
- Microsoft.DotNet.CodeAnalysis - 5.0.0-beta.20071.3
- Microsoft.DotNet.GenAPI - 5.0.0-beta.20071.3
- Microsoft.DotNet.XUnitConsoleRunner - 2.5.1-beta.20071.3
- Microsoft.DotNet.GenFacades - 5.0.0-beta.20071.3
- Microsoft.DotNet.Helix.Sdk - 5.0.0-beta.20071.3
- Microsoft.DotNet.RemoteExecutor - 5.0.0-beta.20071.3

We go out of our way (e.g. on Unix queueing work off of the epoll threads) to ensure that arbitrary user code running as part of socket continuations doesn't block those threads and potentially deadlock.  Add a test to help validate this.

This leads us to generate an illegal relocation fixup.

Fixes #1789

* Avoid extra field loads / comparisons in FindFirstChar

If we've already compared the current pos to the end pos as part of a minimum length check, we don't need to repeat it again later.  We can also read from locals rather than fields more than we are to save redundant field reads.

* Reduce branches in Boyer-Moore negative switch table

It's often the case that lots of negative branches have the same value.  We can coalesce them.

* Address PR feedback

* Validate key on HMAC classes.

A refactoring in HMACCommon caused null keys to be implicitly converted
in to empty spans. This lead to a null key being used as an empty key.

* Use assertion helper to test parameter name.

This causes an additional dependency of mono on libintl which we didn't have before.
Reported by a user on gitter, it's problematic on macOS since it makes the mono binary depend on the libintl we ship in the Mono .pkg.

It was introduced in Mono 6.6 by https://github.com/mono/mono/commit/18e0ebfe89be0a175d2f904b9bb1ec6816daa318

* Enable Mono in default build

* Integrate Mono into the build system

* Fix System.Private.CoreLib build in Mono

Broken by https://github.com/dotnet/runtime/commit/9c82a36c23235c4d50954cb33a4d5d89b787a1aa

* Disable Windows test runs

Fails due to https://github.com/dotnet/runtime/issues/1933Co-authored-by: NViktor Hofer <viktor.hofer@microsoft.com>

* Exposed casting cache to managed code
* Implemented a managed version of cache lookup
* Moved `JIT_IsInstanceOfAny` and `JIT_ChkCastAny`  to managed code as the first ones to move.
* Skip managed JIT helpers in exception stack traces and debugger
* Managed `JIT_IsInstanceOfInterface`
* All other cast helpers are managed.

Fixes:https://github.com/dotnet/coreclr/issues/27931

And add tests.

Largely, the intent of this change was to reduce the number of temporary readers required for deeply structured payloads (`ReadSequence` returns a new reader), while still maintaining the better usability of the class; and, frankly, to understand what the impact of splitting functionality into "bare metal" and "more usable" pieces was.

```
foreach (file in AsnReader.*)
{
    Copy/paste the entirety of the `partial class AsnReader`;
    Change the top version to say ref partial struct AsnValueReader;
    Replace all AsnReader calls in the top version to say AsnValueReader.
    Replace all ReadOnlyMemory in the top portion with ReadOnlySpan;
    Remove ArraySegment overloads from the top portion (when present);
    Rewrite the bottom portion to open a ref reader at the state the memory is tracking and defer work into the ref reader;
    Run all the existing tests to ensure that nothing broke in that piece;
}
```

Once that was done, I changed the asn.xslt to generate all of the decoding in terms of AsnValueReader.  This didn't change field generation from ReadOnlyMemory to ReadOnlySpan (and the types from struct to ref struct)--a change that could be done later--but instead added a new ReadOnlyMemory input parameter so it can use Overlaps to slice the memory as appropriate (with a fallback of ToArray()).

While I was editing asn.xslt I fixed probably all of the whitespace errors it generated.  I still left the "stylecop, have no opinion about whitespace" pragma since the generator isn't run as part of most people's (or the official) builds.  This also turns on the nullability checks in all of the generated structs.

* Add additional error checking for mainv1, mainv2 tests

These have been silently failing due to mainv1.exe and mainv2.exe
changing to be built at mainv1.dll and mainv2.dll without
corresponding changes in the project files, due to insufficient
testing in the script.

Add this additional testing.

* Add more error checking

* Fix script errors in mainv1, mainv2 tests

A while back, tests were changed from building .exe to building .dll files
but these were not updated. Fix that.

* Reconcile handling of EH vars

Modify `BasicBlock::hasEHBoundaryIn()` and `BasicBlock::hasEHBoundaryOut()` to reflect what liveness is doing, and adjust the register allocator code appropriately.

It might make sense to extract the code that's basically the same, except that the register allocator doesn't need the `finallyVars` except as validation in the `DEBUG` case.

Fix #1786

* Add readme for Mono specific version of SPC

* Update src/mono/netcore/System.Private.CoreLib/README.md
Co-Authored-By: NStephen Toub <stoub@microsoft.com>

It doesn't seem like we validate anything for those and `IsRuntimeDeterminedSubtype` check is rather expensive.

Not perf-critical, just some cleanup of low hanging fruit.

- Unify more of CoreLib interop files
- Replace manual interop with regular managed APIs where possible
- Delete unused code

Contributes to #1232

* FinalCoreFXRenames

The last of the CoreFX renames.

* Update DirectorySearcher.cs

Fixed typo in DirectorySearcher.cs

* Update TestClasses.SimpleTestClassWithObjectArrays.cs

This fixes the expected value of the tests to runtime, instead of corefx.

* Update PersistedFiles.Names.Unix.cs

Adds a note to not update the corefx reference.

Workaround AzDo issue when evaluating Build.SourcesDirectory variable  in a docker container (#1982)

* Workaround AzDo issue when evaluating Build.SourcesDirectory variable in a docker container

* Only use env var when in a docker container

Moves policydata to a PAL struct so it can be passed without creating and discarding the X509Extension objects.

* making ilsdk crosstarget

* editing the comment

The term platform was ambiguous. Migrate to using common terminology for
cross compilation.

Host is the platfrom which will execute the code
Target is the platform which will be debugged or for which code will be generated.

In most cases HOST == TARGET.  The exceptions are the cross component crossgen
tools and the future cross DAC.

* Add ThrowHelper, and clean up some style

Trying to streamline main path to the engine, ensuring helpers can be inlined, reducing boilerplate, etc.  And as long as ThrowHelper was being used in some places, used it in others where it didn't require adding additional methods.

Also cleaned style along the way.

* Streamline the Scan loop

The main costs remaining are the virtual calls to FindFirstChar/Go.

* Enumerate matches with a reusable match object in Regex.Replace/Split

The cost of re-entering the scan implementation and creating a new Match object for each NextMatch is measurable, but in these cases, we can use an iterator to quickly get back to where we were and reuse the match object.  It adds a couple interface calls per iteration, as well as an allocation for the enumerator, but it saves more than that in the common case.

* Use SegmentStringBuilder instead of ValueStringBuilder in Replace

A previous .NET Core release saw StringBuilder in Regex.Replace replaced by ValueStringBuilder.  This was done to avoid the allocations from the StringBuilder.  However, in some ways, for large input strings, it made things worse.  StringBuilder is implemented as a linked list of builders, whereas ValueStringBuilder is contiguous memory taken from the ArrayPool.  For large input strings, we start requesting buffers too large for the ArrayPool, and thus when we grow we generate large array allocations that become garbage.

We're better off using a simple arraypool-backed struct to store the segments that need to be concatenated, and then just creating the final string from those segments.  For the common case where there are many fewer replacements than the length of the string, this saves a lot of memory as well as avoiding a layer of copying.

* Replace previously added enumerator with a callback mechanism

The delegate invocation per match is faster than the two interface calls per match, plus we can avoid allocating the enumerator and just pass the relevant state through by ref.

* Remove unnecessary fields from MatchCollection

* More exception streamlining and style cleanup

* Address PR feedback, and fix merge with latest changes

* Optimize DateTime decomposition in CoreLib
Add uses of DateTime.GetDate (renamed from GetDatePart) where appropriate
Add DateTime.GetTime method to eliminate duplicate computations

* Remove unused arithmetic from DateTime.GetTime

The tests used by PlatformHandlerTest moved to Common/tests in order to share them between System.Net.Http and System.Net.Http.WinHttpHandler.
The added conditions correspond to the state before WinHttpHandler removal. They're just based on IsWinHttpHandler instead of UseSocketHandler.
Some of the code must be conditionally compiled since there is no usable common base class for HttpClientHandler and WinHttpHandler. Other issues solved by introducing WinHttpClientHandler for testing purposes. It corresponds to HttpClientHandler.Windows.cs code from before its removal.

We're currently generating the code for a one / not one / set ? quantifier (zero-or-one) as a loop, when it can actually just be a conditional check.  This adds a special path for that case.

(I've also added another reduction test for alternation, and tweaked the codegen for a successful match to touch fields less.)

Follow-up from #1788.

Add padding to `AssertionDsc` so that the `iconFlags` no longer overlap with `lconVal`. Assert that `iconFlags` is never set for an O2K_CONST_LONG assertion.

Also remove an arm-only handle block that should now be redundant.