Handle failures during integration test remoting cleanup

Fix race condition in symbol start action execution

Fix failure to close the C# Interactive window in tests

Skip M.CA.CS.Symbol.UnitTests on dev16.0.x

Guard against entry added from another thread.
Fixes internal VSO bug [#700302](https://devdiv.visualstudio.com/DevDiv/_workitems/edit/700302)

Do not try to convert interpolated string format specifiers into virtual chars

Skip an integration test and an assert that is firing frequently on d…

Merge dev15.9.x to dev16.0.x

Change analyzer executor to do an intersection with the given span 

Merging features/NullableReferenceTypes to dev16.0.x

For cases where the requested span is (x, x), try using span
intersection rather than contains.

That should cover all the cases for requesting the diagnostics
at caret

Fixes #27703

Workaround for msbuild bug https://github.com/Microsoft/msbuild/issues/3825.

Add a overload to AsynchronousViewTaggerProvider for TypeScript

Fix for InvalidCastException in "Invert If" refactoring

Also fix the IDE helper to get value usage info, which fixes the MakeFieldReadOnlyAnalyzer

Fixes #29373
Fixes #30175

The addition of IThreadingContext to this type's constructor broke
TypeScript, which they already have a build for that deals with the
change. However it requires a simultaneous insertion which is proving
difficult to achieve. Adding this overload (which is admittedly a total
hack) allows TypeScript to continue functioning even with Roslyn's
change.

moved to newer optimization package

Conservatively apply logical not operator to an expression being negated if it is not a binary operation.

Fixes #29434