This seems to be a popular call among analyzers, especially XUnit. It's a
reasonable way to acquire a well-known analyzer type, but analyzers often
don't save the resulting symbol. This causes significant CPU work to be done
repeatedly as XUnit looks for the same symbol over and over, passing in the
same type name each time.

A very small, simple cache seems to solve the problem without requiring any
changes on the XUnit side.

* Add API bool Compilation.IsSymbolAccessibleWithin(
            ISymbol symbol,
            ISymbol within,
            ITypeSymbol throughType = null)
Also correct comments that incorrectly imply that inaccessible methods can be a member of a method group.
Fixes https://github.com/dotnet/roslyn/issues/24518
Fixes https://github.com/dotnet/roslyn/issues/23842

Followup to #26325 and #26330. This PR updates the IDE to forward certain helpers to these more efficient implementations.

This helps things out by more quickly being able to determine if a type even contains a member with name, and thus whether or not it should even be hydrated into a symbol and have its members created. Previous we would have to do a linear scan on all the members in a type to determine this. Now this data is in a set which can be queried much more efficiently.

Also add
- CommonConversion.IsImplicit
- Compilation.HasImplicitConversion
Fixes #9461

* Handle lock statement in control flow graph
* Improve handling of IConditionalAccessOperation used at the statement level.

* Produce errors on invalid pdbpath supplied to compiler

* More tests

* Refactor Windows PDB writer

- Update pe writer to not rely on updated System.Reflection.Metadata for arm64 support
  - Instead of using System.Reflection.Metadata support, write the PE as x64, and then
    modify it to have the correct machine.
- Add support for determistic PE generation with Arm64 platform
  - ensure that the hash used for timedatestamp is based on the contents with the Arm64 pe flag set
- Update resources to describe arm64 as a viable platform switch

* Include PDB Checksum in Debug Directory

* Xlf files

* Add more validation

* Fix tests

* Fix xplat test

* Remove data signature

Fixes #23464

RunCore previously had a mix of diagnostic reporting methods including
lists of Diagnostics, lists of DiagnosticInfos, ConcurrentQueues of
Diagnostics, and just printing things directly to the console. This
commit tries to simplify things by moving to using Diagnostics and
DiagnosticBags wherever possible in the compile+emit phase of RunCore.

This reverts commit 27dc60f5.

* Compare lines instead of using AssertXml when validating PDBs.

AssertXml doesn't validate ordering.

* Reorder expected PDB XML nodes to match actual order

* Update to the latest Microsoft.DiaSymReader.* packages.

* Enable embedding sources to Windows PDBs

Enable few more rules and fix issues identified these rules.

Also added issue IDs for the disabled rules due to lack of a fixer/fix all experience.

The PDB path which is written into the PE file should respect the
`/pathmap` option passed to the compiler.  This is necessary to ensure
that PEs can be deterministic when built from different source paths.

The feature flag `pdb-path-determinism` is being kept for the time
being.  Even though it's a feature flag it still seems inappropriate to
break customers in a point release.  Deferring the removal until the
next major release to give customers time to react.  This issue tracks
removing the flag:

https://github.com/dotnet/roslyn/issues/19592

closes #9813

* Ref assemblies make a best effort to emit with determinism
* Fixing CopyRefAssembly message output
* CopyRefAssembly logs when input isn't ref assembly
* CopyRefAssembly does assembly redirect.
* Compact error codes for C# 7.1