Use * instead of Unpack[...] in messages when targeting Python 3.11 or later

[JukkaL]

On Python 3.11 and later it seems better to use the native syntax with * instead of Unpack[...] in various messages.

This is the current behavior:

x: tuple[int, *tuple[int, ...]]
# note: Revealed type is "tuple[builtins.int, Unpack[builtins.tuple[builtins.int, ...]]]"
reveal_type(x)

I'd expect the note to look like this:

Revealed type is "tuple[builtins.int, *builtins.tuple[builtins.int, ...]]"

[ilevkivskyi]

Yeah, we already do this for error messages, see https://github.com/python/mypy/blob/master/mypy/messages.py#L2519-L2520. I just noticed one tricky thing btw: Unpack can be also used for TypedDict unpacking in **kwargs, in that case we need to keep it as Unpack[...].

[AlexWaygood]

See also python/cpython#104048 and python/typing_extensions#163, where we changed the runtime repr of Unpack to reflect that it could now be used in a PEP-692 context as well as a PEP-646 context