Update/fix XML docs for generated types

[cremor]

Rationale

The XML documentation of the generated types - at least the types which are directly used by developers - should match the documentation which is available on learn.microsoft.com and in the IDE when the "native" types are used.

I haven't checked all types, but I've found differences in:

• CallerArgumentExpressionAttribute
  • class summary
  • class remarks
  • ctor paramter
  • property summary
• Index
  • class summary
  • class remarks
  • various small differences in members

[0xced]

I guess this is somewhat linked to #88.

[gregsdennis]

For my use, I don't really care if the docs match the types. I have XML doc generation enabled in my libs, and I get warnings on any public code that doesn't have XML comments. I'd be happy with anything, even empty, but I agree that it should be whatever MS has.