[clang-tools-extra] [clangd] Augment code completion results with documentation from the index. (PR #120099)

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

> Seems to be template-related.
> 
> test.hpp:
> 
> ```c++
> template <typename T>
> struct templated {
>   // comment
>   void foo();
> };
> struct nontemplated {
>   // comment
>   void foo();
> };
> ```
> 
> test.cpp:
> 
> ```c++
> #include "main.hpp"
> void foo() {
>   nontemplated n;
>   n.f^   // comment is shown
>   templated<int> t;
>   t.f^  // comment is not shown
> }
> ```

Filed https://github.com/clangd/clangd/issues/2290 as a follow-up to track this remaining issue with templated methods.

https://github.com/llvm/llvm-project/pull/120099