Allow `is` and `is` not for direct type comparisons (#7905)
## Summary
This PR updates our E721 implementation and semantics to match the
updated `pycodestyle` logic, which I think is an improvement.
Specifically, we now allow `type(obj) is int` for exact type
comparisons, which were previously impossible. So now, we're largely
just linting against code like `type(obj) == int`.
This change is gated to preview mode.
Closes https://github.com/astral-sh/ruff/issues/7904.
## Test Plan
Updated the test fixture and ensured parity with latest Flake8.
