Basic support for typing_extensions.Annotated.

[brandtbucher]

Closes #7021. This adds basic support for typing_extensions.Annotated. Currently, we just discard all annotations and resolve to the inner type.

Plugins can use get_type_analyze_hook to try to intervene before this step, but most of the arguments that aren't just names or Literal-able values will have already been mangled by this point. Nothing other than the type sees any sort of validation, either. See the issue discussion for more on this.

[msullivan]

Thanks! This looks great. We'll need to package up the expressions into a RawExpressionType like discussed in the issue before this is likely to be truly useful to things that actually want to use Annotated, but accepting it is an important first step.