[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
20 files changed