[clang-tidy][docs] Rename bugprone check docs to Markdown [3/4] (#214421) 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 3/4 of the remaining `bugprone` check documentation. The rewrite is provided by the next PR in this stack. GitOrigin-RevId: a7307132c575ff4c087dc4fc59487af984a95ac6