macros: Expand macro invocation properly in type contexts

Macro invocations can be present where the language expects types. Thus,
we need to add a new type of parsing context, a new transcriber, as well
as a new way to extract types from the AST Fragments. This adds a lot of
"expansion places" in the attribute visitor, as types can be present in
a wide variety of constructs

Author: CohenArthur