This enables basic support for applying top-level nullability to
parameters and the return types when generating methods.

Fixes https://github.com/dotnet/roslyn/issues/30319

* Fixes 14077

* Respond to feedback

* More tests

* Add FallbackNamingRule for parameters

* Fix default parameter naming rule

* Use parameter naming style, add tests

* Use 'default' over 'default(T)'

* Update BreakpointSpans.cs

* Update DeclarationNameCompletionProvider.DeclarationInfo.cs

* Update BreakpointSpans.cs

* Update DeclarationNameCompletionProvider.DeclarationInfo.cs

* Update DeclarationNameCompletionProvider.DeclarationInfo.cs

* Update DeclarationNameCompletionProvider.DeclarationInfo.cs

* Update BreakpointSpans.cs

Adjust various places outside of compiler to account for the fact that ArgumentSyntax.Expression can be null.

Fixes #12147.

Offer 'generate constructor' when a derived type doesn't include a delegating constructor to it's base type

     Background:

     As discussed in the dev team all hands all code under the GitHub dotnet foundation is using a single process for contribution, API review, infrastructure and coding style. The idea is to present a unified view to our customer and give them a single story for contributing to any project under the dotnet foundation.

     https://github.com/dotnet/corefx/wiki/Contributing#c-coding-style

     The coding style transition is automated using a Roslyn based rewrite tool:

     https://github.com/dotnet/codeformatter

     This will be applied in stages across our developer tree. Right now the focus is on the Open directory as this is what is being presented on github. Code owners will be contacted before the transition happens.

     Note: this is a soft style requirement. There are no build errors that come from this change.
 (changeset 1408227)