Extend `unnecessary-pass` (`PIE790`) to include ellipses in preview (#8641)
## Summary
This PR extends `unnecessary-pass` (`PIE790`) to flag unnecessary
ellipsis expressions in addition to `pass` statements. A `pass` is
equivalent to a standalone `...`, so it feels correct to me that a
single rule should cover both cases.
When we look to v0.2.0, we should also consider deprecating `PYI013`,
which flags ellipses only for classes.
Closes https://github.com/astral-sh/ruff/issues/8602.