This allows this to be loaded downlevel so tests don't fail on
Preview 3.

Downgrade System.ValueTuple to 4.0.1-beta-24425-02

Include .vsdconfig files in Roslyn CoreXT package

Use new base-class to simplify code.

Add a new feature that suggests using an 'out-variable' when possible.

Use the actual severity asked for in 'Use Throw Expression'.

Disable tests failing because of: https://github.com/dotnet/roslyn/issues/14380