[clang-tools-extra] [clangd][HLSL] Add hover support for vector swizzle and matrix element access (PR #212741)

[via cfe-commits]

github-actions[bot] wrote:

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

* 3259 tests passed
* 34 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/Hover/HLSLVectorAndMatrixSwizzle</summary>

```
Script:
--
C:\_work\llvm-project\llvm-project\build\tools\clang\tools\extra\clangd\unittests\.\ClangdTests.exe --gtest_filter=Hover.HLSLVectorAndMatrixSwizzle
--
unknown file
SEH exception with code 0x3221225477 thrown in the test body.
Stack trace:

Google Test trace:
C:\_work\llvm-project\llvm-project\clang-tools-extra\clangd\unittests\HoverTests.cpp(5368): 
            typedef float float3 __attribute__((ext_vector_type(3)));
            void main() {
              float3 v;
              float3 s = v.^[[xyz]];
            }
          


```
</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/212741