[clang] fix(clang/**.py): fix invalid escape sequences (PR #94029)

[Donát Nagy via cfe-commits]

https://github.com/NagyDonat requested changes to this pull request.

Despite the many force pushes, there patch did not change substantially (I think they were just rebases), so my review from 2025 still stands:
- The changes in `clang/docs/tools/dump_ast_matchers.py` are – to my best understanding – unnecessary and counterproductive. @e-kwsm Why do you want to change these? Is there some justification that I don't see?
- The change in `clang/test/Analysis/check-analyzer-fixit.py` is justified, but I still prefer the other approach that I have suggested in an inline comment. (The two approaches are correct and functionally equivalent, but my suggestion is more idiomatic.)

https://github.com/llvm/llvm-project/pull/94029