These helpers are used to report names of things in warnings. The functional changes are:
* For method parameters, use the parameter name if available (and only if not fallback to the #1 notation)
* For property accessor methods, use the C# naming scheme, so for example Type.Property.get instead of Type.get_Property.

Both of these changes are in preparation to bring NativeAOT closer in behavior to ILLink and the trim analyzers.

For this I moved some of the helpers to the common shared code.

Some unrelated code cleanup as well.

Co-authored-by: Michal Strehovský <MichalStrehovsky@users.noreply.github.com>