[clang-tidy][docs] Rename bugprone check docs to Markdown [4/4] (#214426) 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 4/4 of the remaining `bugprone` check documentation. The rewrite is provided by the next PR in this stack. GitOrigin-RevId: b272bfe2177312f07c3d0ca08e80cdb5a1d6bdff