Set up `type_checked` tag for internal type hint migration #7886
Per #6742, we will be incrementally adding type hints to Pants.
We need some way to mark to our CI that the target should be checked against, to make sure that any gains we make in type hints are actually enforced.
Introduce a new tag
Also introduce a helper script
Alternative solution considered: centralized whitelist file
It was decided that a decentralized system will work better in this particular case, for some of these reasons: