[clang-tools-extra] [clangd] Add go-to-definition support for fields in offsetof expressions (PR #192953)

[Aleksandr Platonov via cfe-commits]

https://github.com/ArcsinX commented:

It seems to work not quite correctly on nested structures.
```c
struct A {
  struct {
   int c;
 } B;
};

int x = offsetof(struct A, B.c);
```
- Hover on `B` or `c` shows information about `B`
- GTD on `B` (or `c`) returns two items (definitions of `B` and `c`)

https://github.com/llvm/llvm-project/pull/192953