[clang-tidy][docs] Rename bugprone check docs to Markdown [2/4] (#214418) Tracking issue: #201242 See the [migration guide] for more information. [migration guide]: https://llvm.org/docs/SphinxQuickstartTemplate.html#markdown-migration-guidelines This is the mechanical rename for part 2/4 of the remaining bugprone check documentation. The rewrite is provided by the next PR in this stack. GitOrigin-RevId: 997fd9c559bb8584fdf437b28404f9d2565c3b8e