This reverts commit 054509fd, reversing
changes made to fc11e8ad.

Add non-test IVT for project system test assemblies

Merge master to dev15.6

Support all roslyn languages in Formatter.FormatAsync(Document)
Fixes #20285

Unify our build logic

Source packages cleanup

Validating params even if they aren't last
Fixes #18875.

This is to prevent misleading errors like "cannot convert from 'typeA'
to 'typeA'" https://github.com/dotnet/roslyn/issues/18875

* Error CS0503 shows the correct modifier target

Fade out unreachable code, and provide code-fix to remove unreachable code.

Properly push events to the OOP side so that we know when things like solution-closing happens.
Fixes #19768

Intern the strings we create for our SyntaxTree index.

Nugetize shared code

Upgared MSBuild / vswhere versions

Correct the error message in our NuGet package

Remove the AnalyzerManager singleton to prevent storing analyzer exec…

Rename Microsoft.CodeAnalysis.Metadata project to Microsoft.CodeAnalysis.Debugging to match the namespace

The error message in our compilers MSBuild NuGet package claims to support MSBuild 14.0. The actual version we support is 15.0.

Include Commit in our NuGet package

Change our low level tooling which is obtained via NuGet to be tracked
in the same way other NuGet packages are tracked.