Fix a crash caused by an improper reuse of lambdas from return inference cache.

Ensure that CPS property setters also invoke the code within ExecuteF…

Similar change as to TestUtilities.  Insteading of having two
independent projects with shared sources there are now a portable and
desktop only version.  The desktop version references the portable one.

Clean up the remaining solutions to have the utilities included.

Fix the factored out runtime code to properly execute the compiler
compiled test code in AppDomains.

Code move before refactoring it.

The Compilers.sln solution is compiling again and tests which don't
require AppDomain support are running again.  There is a bit of work
that is needed for AppDomains that I want to separate out.  In
particular the separation to portable means we have to redo some of the
serialization code.

The TestUtilities project should be our portable unit test helper.  This is part one of rearranging our sources to reflect that reality.  I'm separating it out because it involves a significant code move that
will make the actual rework part harder to review.

This is the project which will hold the CoreClr capabilities for our test infrastructure.  In particular it will hold the code for using AssemblyLoadContext to manage our isolated test boundaries.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems?id=296550.

Updating the open vs-integration tests to run by default.

Add test for specified behavior of a virtual method invocation (via a binary compatibility scenario). (#16055)

* Add test for specified behavior of a virtual method invocation (via a binary compatibility scenario).

Format the coalesce expression we produce.

Fixes #16025

Enforce DocumentationFile is a centrally controlled property

This property is controlled by our central build targets.  It shouldn't be used in indivdidual projects anymore as it can lead to bugs.  See the following PR from @KirillOsenkov for an example of how this leads to bugs

https://github.com/dotnet/roslyn/pull/15880

Remove EmitContext from ITypeReference.TypeCode

Fix ability to run portable tests with TDD, F5, etc ... 

Combine duplicate methods

This fixes the foreground asserts from CPS property setters. Fixes https://github.com/dotnet/roslyn-project-system/issues/1000.

Fix XML doc name for BasicInteractiveEditorFeatures

Cleaning up the open integration framework