Refactor clang doc comment structure (#142273)
This patch refactors CommentKind handling in clang-doc by introducing a
strongly typed enum class for better type safety and clarity. It updates
all relevant places, including YAML traits and serialization, to work
with the new enum. Additionally, it enhances the Mustache-based HTML
generation by fully supporting all comment kinds, ensuring accurate
structured rendering of comment blocks. The changes simplify future
maintenance, improve robustness by eliminating unchecked defaults, and
ensure consistency between generators.
Fixes https://github.com/llvm/llvm-project/issues/142083
