* origin/stabilization:
  Fixes REPL initialization and SourcePaths handling
  Delete unused WaitHelper.WhenAll
  Don't call PumpingWaitResult for the result of GetSyntaxTreeAsync

Fixes REPL initialization and SourcePaths handling

Don't call PumpingWaitResult for the result of GetSyntaxTreeAsync

Use new null-conditional operator in CSharpExtensions

* origin/stabilization:
  Use ?. since we have the technology
  Don't crash when invoked from an accessor
  Correct casing of test method

Fix a race condition in AsyncQueue.EnqueueCore

Fix generate end construct when invoked on an accessor

Added quotes to filepath variables in GenerateCompilerInternals.targets

* origin/stabilization:
  This change increases the severity of analyzer exception diagnostic (AD0001), generated when an analyzer throws an exception, from info to a warning. Additionally, its descriptor is now reported as a supported diagnostic descriptor of the compiler analyzer, which ensures that it shows up in the ruleset editor.

Only perform semantic classification for what's actually in view.

Fix a race condition in AsyncQueue.EnqueueCore

Moved MiscDiagnosticUpdateSourceTests to use Async to reduce timing issues

This change increases the severity of analyzer exception diagnostic

Cause: We are seeing intermittent deadlocks during build on linux machines running our test suites. The deadlock happens when one thread invokes AtomicSetFlagAndRaiseSymbolDeclaredEvent, and succeeds in setting the flag and invokes SymbolDeclaredEvent while holding onto the lock. The task scheduler decides to inline the event processing, which attempts to execute analyzers while holding onto the _diagnosticLock. Another thread meanwhile is already executing analyzers and calls back into the compiler and is waiting on _diagnosticLock.

Fix: Fix the AsyncQueue.EnqueueCore method to invoke SetResult on the waiter task completion source on a separate task. This ensures that no external code executes while attempting to Enqueue a compilation event, and hence cannot deadlock.

Testing: All tests pass locally.

Fixes #https://github.com/dotnet/roslyn/issues/6098

Include the actual underlying exception in "failed to run".

Introduce Project.HasCompleteReferencesAsync

Set State.WaitingForInput in PrepareForInput

Fixes #5964

Remove left-over package.config refs

Added supports clauses to project.json to fix #6073

Do not perform commit when there are unterminated string literals.

[AskMode] VisualBasicUnboundIdentifierDiagnosticAnalyzer fix
Fixes #5920

[ask mode] Rename WithCompilationScriptInfo -> WithScriptCompilationInfo

Test `EmitSequenceOfBinaryExpressions_03` in VB is failing in signed builds.