[clang-tools-extra] clangd: Extend reference search with constructor calls through forwarding (PR #169742)

[via cfe-commits]

github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Windows-->
# :window: Windows x64 Test Results

* 2995 tests passed
* 30 tests skipped
* 1 test failed

## Failed Tests
(click on a test name to see its output)

### Clangd Unit Tests
<details>
<summary>Clangd Unit Tests._/ClangdTests_exe/BackgroundIndexTest/ConstructorForwarding</summary>

```
Script:
--
C:\_work\llvm-project\llvm-project\build\tools\clang\tools\extra\clangd\unittests\.\ClangdTests.exe --gtest_filter=BackgroundIndexTest.ConstructorForwarding
--
C:\_work\llvm-project\llvm-project\clang-tools-extra\clangd\unittests\BackgroundIndexTests.cpp:283
Value of: getRefs(Idx, Constructor->ID)
Expected: has 1 element that has a first field that is anything, and has a second field that has 2 elements and there exists some permutation of elements such that:
 - element #0 file u r i (F: "unittest:///root/header.hpp"), and
 - element #1 file u r i (F: "unittest:///root/test.cpp")
  Actual: { (D13ED938BA596D1E, { unittest:///root/header.hpp[8:6-8:10):Def, Spelled }) }, whose element #0 doesn't match, whose second field does not match, which has 1 element


```
</details>

If these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the `infrastructure` label.

https://github.com/llvm/llvm-project/pull/169742