[clang-tools-extra] [clangd][HLSL] Prevent RootSignature internal identifier leak on hover (PR #214955)

[Aleksandr Platonov via cfe-commits]

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ArcsinX wrote:

It looks like this patch can be single-line
```diff
+ if (!AST.getLangOpts().HLSL || !llvm::isa<RootSignatureAttr>(A)) {
- {
```
 
And add comment about why pretty-print is not acceptable here

https://github.com/llvm/llvm-project/pull/214955