…features/function-pointers

* upstream/master: (465 commits)
  Stop specifying Rich Nav's version of dotnet
  Fix nullable reference warning
  Fix up some calls to SymbolKey.Resolve now that it's annotated
  Remove try/catch of ArgumentException
  Null annotate SymbolKey
  Annotate Location.IsInSource as ensuring SourceTree is non-null
  Fix nullable annotation of Compilation.CreateErrorTypeSymbol
  Update null state for add/remove on field-like events (#46477)
  Throw IndexOutOfRangeException from BitVector.this[int] if index < 0 (#46627)
  Delete some dead support for changing legacy options
  Delete our use of Microsoft.VisualStudio.CodingConventions
  Fix crash in the preview of a code action that modified an .editorconfig
  Move null check above where the variable is used (#46558)
  Add integration test to configure diagnostic severity via editorconfig
  Disable a few Mac tests
  Consider nullability in conversion to constraint type (#46405)
  Added interpolated strings and tests
  Introduce request context (#46557)
  Simplify NativeIntegerAttribute encoding (#46522)
  Update extension getenumerator status. (#46607)
  ...