Ignore preview status for fixable and unfixable selectors (#9538)
## Summary
Right now, if you run with `explicit-preview-rules`, and use something
like `select = ["RUF017"]`, we won't actually enable fixing for that
rule, because `fixable = ["ALL"]` (the default) won't include `RUF017`
due to the `explicit-preview-rules`.
The framing in this PR is that `explicit-preview-rules` should only
affect the enablement selectors, whereas the fixable selectors should
just include all possible matching rules. I think this will lead to the
most intuitive behavior.
Closes https://github.com/astral-sh/ruff/issues/9282. (An alternative to
https://github.com/astral-sh/ruff/pull/9284.)
