[clang-tools-extra] [clangd] Collect comments from function definitions into the index (PR #67802)

[Nathan Ridge via cfe-commits]

https://github.com/HighCommander4 approved this pull request.

Thanks! The patch looks good to me. And the index size measurements reported in [this comment](https://github.com/llvm/llvm-project/pull/67802#issuecomment-1923778262) look good as well, thank you for taking them.

https://github.com/llvm/llvm-project/pull/67802