Needed to have net framework 40 helpers as it's required by some tests.

This unifies our API naming convention. When standard is in the name
then we are using the netstandard2.0 API set and when it is not then it
is the simple desktop mscorlib46.

Both variants are necessary for CompileAndVerify style functions because
many of our tests that use it can only run on desktop or simply need to
have some of the netstandard2.0 API set missing.

This unifies the API surface avalaible to code passed to CreateStandardCompilation
between CoreClr and Desktop execution to NetStandard2.0.

Ideally both would compile against NetStandard2.0 under the hood. But there are some
code execution limitations right now (no facades) that make that hard. For now just
ensuring the same API surface which will make it easier to port tests over.

* Permit selecting an instance from a type in a sub-expression in nameof(...)

Fixes #20600

Skipping PasteCommandWithOutInteractiveFormat test

Skipping TestSelection test

Skipping TestRegionCompletionCommitFormatting test

* first refactoring to add connection pool

* pool added

* removed usage of KeepAliveSession which solely used as performance benefit favoring perf over complexity.

now with pool, there is no perf advantage by KeepAliveSession. it should be only used when one wants to make connection stateful.

* change remote call signature since solution is now set automatically

* fixed test failures

* made some constant an options. and made pool off by default

handle pool shutdown better

* now turn it on by default

* PR feedbacks

* address more PR feedbacks

* more comments

* renamed ConnectionPool to ConnectionManager. people seems confused by name too much. pool is just one of thing it does, it owns connection management in general.

* PR feedbacks

* change Contract.Fail to Contract.Require so that it doesn't crash VS when OOP is killed explicitly by users.

* PR feedbacks

* address feedbacks

* put finalizer under debug flag

Fix running unit tests in MicroBuild

We were launching xunit by ShellExecute'ing not the procdump executable,
but rather the folder that contained the procdump executable. That
really doesn't work well, it turns out.

Fix CSharpFormattingOptions csharp_space_around_binary_operators key

Merge pull request #24173 from MaStr11/SuppressIDE0041_UseIsNullcheck_ForUnconstraintGenericParameters

Suppress 'IDE0041 Null check can be simplified' for unconstraint generic parameters.

GetHashCode code generator should produce code that doesn't overflow in checked mode.

Merge dev15.6.x to dev15.7.x

Do not suggest var when it change static type of the variable in foreach statement

Localization test failures 2

case 'type constraint': no fix offered
case 'reference constraint': C# use '==null' instead of  'is null'
default: C# 'is null', VB 'IsNothing'

Enable VerifyCodeRefactoringOffered tests

Enable ExtractViaCodeActionWithMoveLocal

Fixes issue #20355?

Is there something special about this bug or am I missing something? There's just an extra space that needs removed, right?

Enable xUnit xml output generation on microbuild