#945509 Support ref readonly parameters

[nickwalkmsft]

Work item: https://ceapex.visualstudio.com/Engineering/_workitems/edit/945509

Add support for correct rendering of "ref readonly" parameter in C# method signature documentation.

Added one unit test and also verified output against the case mentioned in the work item (https://learn.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.unsafe.asref?view=net-8.0#system-runtime-compilerservices-unsafe-asref-1%28-0@%29 should render with scoped ref readonly T source instead of scoped ref T source.

I couldn't get the C++ tests running but they appear to be out of scope here.