[clang] [Index] Report references through UsingType (PR #228823)

[Fangrui Song via cfe-commits]

MaskRay wrote:

```
# Build clang libraries used by ccls
ninja -C /data/out/debug clang clangIndex clangTooling clangFormat profile

# Build https://github.com/MaskRay/ccls
 cmake -H. -Bout/debug -G Ninja -DCMAKE_BUILD_TYPE=Debug -DCMAKE_CXX_COMPILER=$HOME/Stable/bin/clang++ -DCMAKE_EXPORT_COMPILE_COMMANDS=On -DCMAKE_PREFIX_PATH="/data/out/debug;/data/out/debug/tools/clang" -DCMAKE_EXE_LINKER_FLAGS=-lmimalloc
```

Before:
<img width="208" height="260" alt="screenshot-20261003-220631" src="https://github.com/user-attachments/assets/b850d109-6597-4c90-8999-109b8deb8845" />

After:
<img width="208" height="260" alt="screenshot-20261003-220609" src="https://github.com/user-attachments/assets/90090f35-a8b4-4bea-b044-62f03a0cd63b" />


https://github.com/llvm/llvm-project/pull/228823