Use `TypeAlias` in code where types are declared
After introducing `TypeAlias` in `_typing.py`, goal of this PR is to use it in any other source files that are creating types in this way.  ~~Also, make all of those types private.~~

I believe that I caught them all via some searching, but may have missed a few.  Couldn't find a rule that enforces use of `TypeAlias`.  Note that in 3.12, the recommendation is to do a `type` declaration, which is probably why there isn't such a rule.

@rhshadrach are we good to merge this? Thanks @Dr-Irv 