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

[Christian Kandeler via cfe-commits]

ckandeler wrote:

I have removed the extra Symbol member and extended the Flags enum instead.
I benchmarked with Qt as the test project (qtbase, to be exact), which is heavily documented and has all its function documentation in the cpp files, so it should provide an upper bound on the effects of this patch.
Index size before this patch : 68MB on-disk, 552MB in-memory
With original patch (extra Symbol member): 70MB/576MB
With latest patch set: 70MB/564 MB
I only did one measurement each, so I don't know if there might be unrelated fluctuations there.

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