[clang-tidy][docs] Rewrite bugprone check docs to Markdown [2/4] (#214419)
Tracking issue: #201242
See the [migration guide] for more information.
[migration guide]:
https://llvm.org/docs/SphinxQuickstartTemplate.html#markdown-migration-guidelines
This rewrites part 2/4 of the remaining bugprone check documentation
from reST to MyST Markdown.
AI Usage: This was prepared with rst2myst and GPT5.6-assisted cleanup.
I manually verified that the documentation renders as expected.
Preview site:
https://broken.life/llvm-staging/bugprone-markdown-port/