Preserve raw string prefix and escapes (#15694)
## Summary
Fixes #9663 and also improves the fixes for
[RUF055](https://docs.astral.sh/ruff/rules/unnecessary-regular-expression/)
since regular expressions are often written as raw strings.
This doesn't include raw f-strings.
## Test Plan
Existing snapshots for RUF055 and PT009, plus a new `Generator` test and
a regression test for the reported `PIE810` issue.
