Support PEP 646 syntax for Callable

[ilevkivskyi]

Fixes #15412

Two new things here as specified by PEP 646:

• Using star for an (explicit) type unpaking in callables, like Callable[[str, *tuple[int, ...]], None]
• Allowing suffix items after a variadic item, like Callable[[X, Unpack[Ys], Z], bool]

Implementation is straightforward. Btw while working in this I accidentally fixed a nasty bug, tuple types were often not given any line/column numbers, so if such type becomes a location of an error, it is impossible to ignore.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

[ilevkivskyi]

@JukkaL @jhance The TypeVarTuple PRs start to pile up, I am going to merge some without review to move faster (I am now working on two trickier PRs) unless you have objections.