Begin transition to Microsoft.CodeAnalysis.Testing

Use 'Sentence case' instead of 'Title Case'

Delete suppressions of CA3053

Test convert nullable to non-nullable using custom awaitable

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20117.3

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20116.1

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20115.1

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20114.5

Fixes #41501.

Fixes #41481

Fix for LSP diagnostic bugs

Activate language client during workspace load.

* Annotate NamespaceOrTypeSymbol

* Annotate public model for NamespaceOrTypeSymbol

* Add double checked locking for AdditionalTextFile.GetText.

* Use LazyInitializer

* Use Lazy instead of LazyInitializer

* Make _text readonly

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20113.6

Merge release/dev16.5 to master

The changes made in https://github.com/dotnet/roslyn/pull/41123 fix the
GetHashCode for SubstitutedMethodSymbol for more nullability scenarios,
but end up hashing all generic methods with a non-generic containing
type into the same bucket. This can cause large performance regressions
for the compiler.

This change ensures that substituted symbols which have substitutions
equivalent to their original methods' type parameter continue to be
equal, but substituted methods with different type substitutions are not
considered equal.

Reduce the amount of stack space needed for parsing embedded statements