Implementing parser changes for "ref readonly"

 `readonly ref` local functions, error tolerance in parsing, more tests.

Parse readonly ref parameters

Correclty handle local functions.

Merge branch 'features/readonly-ref' of https://www.github.com/dotnet/roslyn into parse-readonly-ref-parameters

Parsing support for readonly ref returns.

* Syntax model and Parsing
* Support for 7.1 language version - just enough to unblock testing.

Initial check in to start the work on "readonly ref" feature.

Introducing new `RefKind.In` - to represent readonly ref parameters.
Also introduces _very preliminary_  ReturnsByReadonlyRef API to represent readonly ref returns.

Duplicate some existing scoping tests for pattern declarations in declarator arguments, where they are not permitted. (#16804)

* Duplicate some existing scoping tests for pattern declarations in declarator arguments, where they are not permitted.
Fixes #13660

Remove space preventing editorconfig settings from applying to vb files

Downgrade SyntaxVisualizerExtension dependencies

Bump the NuGet moniker to -rc5

We've shipped -rc4 packages to nuget.org, so any future builds should
be versioned higher.

Merging on behalf of @DanMcNultyDev

Add test coverage for Out Vars in global code in remaining executable statements.

Added test to verify intellisense on Enumerable.Join parameter types

Closes #14113.

More pattern matching scope tests

Prevent error on Analyzer project creation

this change prevents an error on RC.3

Add test binding redirect for System.Xml.XmlDocument

changed all caller to call JsonRpc.StartListener once all states are set