Add config option to disable `typing_extensions` imports (#17611)
Summary
--
This PR resolves https://github.com/astral-sh/ruff/issues/9761 by adding
a linter configuration option to disable
`typing_extensions` imports. As mentioned [here], it would be ideal if
we could
detect whether or not `typing_extensions` is available as a dependency
automatically, but this seems like a much easier fix in the meantime.
The default for the new option, `typing-extensions`, is `true`,
preserving the current behavior. Setting it to `false` will bail out of
the new
`Checker::typing_importer` method, which has been refactored from the
`Checker::import_from_typing` method in
https://github.com/astral-sh/ruff/pull/17340),
with `None`, which is then handled specially by each rule that calls it.
I considered some alternatives to a config option, such as checking if
`typing_extensions` has been imported or checking for a `TYPE_CHECKING`
block we could use, but I think defaulting to allowing
`typing_extensions` imports and allowing the user to disable this with
an option is both simple to implement and pretty intuitive.
[here]:
https://github.com/astral-sh/ruff/issues/9761#issuecomment-2790492853
Test Plan
--
New linter tests exercising several combinations of Python versions and
the new config option for PYI019. I also added tests for the other
affected rules, but only in the case where the new config option is
enabled. The rules' existing tests also cover the default case.
