Include generic interfaces in implements clause completion

Show diagnostic nodes in Solution Explorer for CPS-based projects

Guard access to shared resource WordSimilarityChecker.s_pool

Add a language service to find entry points that can be accessed from the CPS project system.

Fix logic that was making us unify different local functions if their signatures matched.

Changes to pattern matching to provide an API more suitable for the platform.

Disabling tests due to flakiness

Classify 'var' in patterns as a keyword.

Support ExperimentalAttribute

PDB fixes and testing

Always show snippets should not exclude non-snippet items

 https://github.com/dotnet/roslyn/issues/18996

Roslyn.VisualStudio.IntegrationTests.CSharp.CSharpErrorListNetCore.ErrorList
Roslyn.VisualStudio.IntegrationTests.CSharp.CSharpErrorListNetCore.ErrorLevelWarning
Roslyn.VisualStudio.IntegrationTests.CSharp.CSharpErrorListDesktop.ErrorList
Roslyn.VisualStudio.IntegrationTests.CSharp.CSharpErrorListDesktop.ErrorLevelWarning

Fix RPS regression due to overly aggressive assertions.

Merge dev15.2.x to master

Fix crash in lightbulbs in projection scenarios.

Don't bother with teh fuzzy matching check if the matcher was created with fuzzy matching not supported.

A previous change of mine moved it so that we try to grab the user's selectoin as the first
thing we do when queried in lightbulbs.  This was to make it so we would not call back into
the UI thread from a BG thread.  Unfortunately, the code i moved was not safe to call if the
query was a projection buffer.  This wasn't a problem previously because there was a prior
check that ran that would cause us to bail out.

I've now reordered things so that the check comes first, and then we get the selection afterwards.