Operation block actions and first system analyzer -- FieldCanBeReadOnly

Use version 2.0.0.0 in future

* origin/master:
  Fixes REPL initialization and SourcePaths handling
  Delete unused WaitHelper.WhenAll
  Don't call PumpingWaitResult for the result of GetSyntaxTreeAsync
  Use new null-conditional operator in CSharpExtensions

* 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/master:
  Update netci.groovy to ensure the %TEMP% directory is created.
  Update netci.groovy to artifact build binaries (excluding intermediate object files).
  Update netci.groovy to override the temp directory for the job.
  Update netci.groovy to override the temp directory for the job.
  Modified GenerateCompilerInternals.targets
  Use ?. since we have the technology
  Don't crash when invoked from an accessor
  Correct casing of test method

* 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/master: (32 commits)
  Convert to an async task.
  Fix a race condition in AsyncQueue.EnqueueCore
  Moved MiscDiagnosticUpdateSourceTests to use Async to reduce timing issues
  Set State.WaitingForInput in PrepareForInput
  Remove file.
  Undo changes.
  Include the actual underlying exception in "failed to run".
  Do not perform commit when there are unterminated string literals.
  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.
  Remove left-over package.config refs
  Added supports clauses to project.json to fix #6073
  Add test for frozen partial semantics and HasCompleteReferencesAsync
  Introduce Project.HasCompleteReferencesAsync
  Call the public GetCompilationAsync versus the internal helper
  Rename TouchDocumentActionForDocument to something clearer
  Add an assert that declaration-only compilations don't have references
  Remove some helper constructors in favor of more explicit code
  Remove runtime type check that doesn't bring any value
  Convert doc comments to real XML doc comments
  PR feedback.
  ...

* 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