[clang] [NFC][HLSL] Move Sema work from `ParseMicrosoftRootSignatureAttributeArgs` (PR #143184)

[Aaron Ballman via cfe-commits]

================
@@ -4963,12 +4958,9 @@ void Parser::ParseMicrosoftRootSignatureAttributeArgs(ParsedAttributes &Attrs) {
       return;
     }
 
-    // Create the Root Signature
-    auto *SignatureDecl = HLSLRootSignatureDecl::Create(
-        Actions.getASTContext(), /*DeclContext=*/Actions.CurContext,
-        RootSignatureLoc, DeclIdent, RootElements);
-    SignatureDecl->setImplicit();
-    Actions.PushOnScopeChains(SignatureDecl, getCurScope());
+    // Perform constructin of declaration
----------------
AaronBallman wrote:

```suggestion
    // Construct the declaration.
```

https://github.com/llvm/llvm-project/pull/143184