Correct grammatical errors in contributing.md

Add useful debug information to OptionKey

Include GetAwaiter() extension method namespace in AddImport suggestions

Merge dev16.0.x to master

Display documentation from associated property/event when showing QuickInfo for get/set and add/remove

Add features to offer using index and range operators.

* Add test for using static with generic argument

* Check using static constraints during Imports validation

* Use CorLibrary from _compilation.SourceAssembly instead of from referenced type

* Use NoLocation.Singleton when @using.UsingDirective is null

* Share conversions object between constraint checks on using static directives

* Add expected diagnostic for using static constraint violation

* Add nested using static generic constraint test

* Add multiple generic constraints in using static test

enable package publishing for dev16 branches

Remove AbstractPackage.ForegroundObject, and its costly initialization

- Reverted FormatCommandHandler.FormatDocument
- Removed option search configuration for code cleanup

Correctly return cached blocks in the IncrementalBinder for things th…

Rearranged query to avoid unnecessary allocations

Reduce set of files copied on official builds

* Fix foreach spilling ref field to a local:
- Fix NeedsByValueFieldAccess to consider if the symbol is ref when it's not writable (i.e. a ref foreach variable: the variable isn't writable but any of its fields should be passed by ref, not value).
- Add a test to show the incorrect behavior is fixed

Fix Linux log publish

https://github.com/dotnet/roslyn/issues/30449

* Check for restricted return types on local functions

* Add test for restricted local function returns

* Add test for local function ref parameters of restricted types

* Add test to demonstrate that local functions can return Span<T>

Only enabled for C#8 or above to avoid suggesting fixes that
break compilation.