Clang-Format uses uses a YAML config file format.

Use YAML language by default for `.clang-format` and `_clang-format`
filenames.
([source](https://clang.llvm.org/docs/ClangFormatStyleOptions.html))
Add `#yaml-language-server: $schema` to `.clang-format` example in C
language docs.

Release Notes:

- Added support for identifying. `.clang-format` files as YAML by
default