TypedDict inheritance is weird in a way that Sphinx can't deal with

easily. TypedDict isn't actually a class itself, and things which

inherit from it get flattened to inherit directly from dict and have a

variety of annotation-only properties for the data inside. Sphinx can

find any documentation attached to those properties, but when one

inherits from another, the documentation for any properties coming from

the parent class gets lost.
This change adds some custom documenter classes to detect when we have

inherited TypedDict members and to scan up the chain using

__orig_bases__ to find docs for inherited members.
This requires Python 3.11+ if using typing.TypedDict. It works for all

versions when using typing_extensions.TypedDict.

Built the RBTools documentation with this and saw that all of our new

*Params definitions had documentation for all members, including ones

  inherited from parent classes.
Ran unit tests.