Follow up to #16965
Fixes #16070

Handles other mypy configuration files and handles precedence between
them. Also fixes few small things, like use in git worktrees

This is a partial revert of #18173 to unblock the 1.15 release

Fixes #18488

I am not waiting for review as the fix is obvious. The only annoying
thing is that we had an exact test as in the repro but it passed
accidentally because we use builtins fixtures.

…8585)

Fixes #18582. Fixes #17396. Supersedes #18351.

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Co-authored-by: hauntsaninja <hauntsaninja@gmail.com>

This makes it more similar to the real typeshed. It is needed to
reproduce tricky failures in tests, e.g.
#18585. If this causes slower tests,
some tests may be switched to `tuple-simple.pyi`.

And add a local pre-commit hook to detect when a PR number in a link
text is different from the link body

Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>

Co-authored-by: Wesley Collin Wright <wesley@wesleywright.me>