[llvm] [lit] Add type hints to builtin_commands (PR #201497)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

I think we can omit `NoReturn`?

We should also be using `from __future__ import annotations` and the more modern `list` and `TypeA | TypeB` syntax so we don't have to switch over once we migrate to Python 3.10.

https://github.com/llvm/llvm-project/pull/201497