Apply modernize-use-starts-ends-with on llvm-project (#89140)

Run `modernize-use-starts-ends-with` on llvm-project. Two instances are
flagged, minor readability improvements, extremely minor performance
improvements.

```
python3 clang-tools-extra/clang-tidy/tool/run-clang-tidy.py \
    -clang-tidy-binary="build/bin/clang-tidy" \
    -clang-apply-replacements-binary="build/bin/clang-apply-replacements" \
    -checks="-*,modernize-use-starts-ends-with" \
    -header-filter=".*" \
    -fix -format
```

I am working on some additions to this check, but they don't seem to
flag any additional cases anyway.