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.

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).

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

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

Fixes #15734

Fixes #15934

Fix the ThrowingTraceListener on portable unit test runs

* moving naming styles types into the workspace layer.
Teaching abstract options serialization service about naming styles.

* Implementing naming styles support for editorconfig

* responding to david's PR feedback

* responding to Jason's feedback

* responding to Jason's feedback part 2

* addressing the latest set of comments from David

* addressing Jason's comments

* addressing Kevin's comments

For the set of assemblies we build on *NIX, we should also be able to
build the coresponding nupkgs so they can be used by other repositories.

On *NIX we have a case sensitive file system, so we need the correct
casing in the .nuspecs.

We should build this tools when we are doing the cross platform build,
they are useful to have as part of the build output.

This fixes a MSB3568 warning during the build of CrossPlatform.sln on
Linux.

See #15751