Pull common FixAll logic into some helper base types that we can use across many of our code style fixes.

Start using Tuples in IDE code.

Run the 'use expression body' analyzer OOP.

MakeRValue should be applied to tuple literals recursively

Clear out our projection buffers when we shutdown the pr eview window to workaround an editor bug.

Merge dev15-rc2 into master

Move to the Dev15 SDK for building VSIX

Fixes:#15198

Cleanup switches

The previous change corrects the last of the double writes.  Can now
remove the work around.

closes #15163

Place CancellationToken parameters last when extracting methods.

Typing <enter> after an interpolated string should not cause 'split string' to invoke.

Allow gramatically correct retests

Report no AssemblyReferences from corlib in EE

Create a code fix that offers to add a reference to System.ValueTuple if it is missing and you use a tuple.

Fixes https://github.com/dotnet/roslyn/issues/14970
Fixes https://github.com/dotnet/roslyn/issues/13375

Remove ByRefReturnErrorTypeSymbol.

Our references were previously a mix of preview 4 and some build between preview 4 and 5.  That was causing build output double writes.

Fix jared