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

[Chris B via cfe-commits]

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@@ -4942,18 +4942,13 @@ void Parser::ParseMicrosoftRootSignatureAttributeArgs(ParsedAttributes &Attrs) {
 
   // Construct our identifier
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llvm-beanz wrote:

I suspect the "Microsoft" bit came from the attribute parsing syntax. HLSL supports "Microsoft"-style attributes (single `[]` rather than C++ `[[]]`.

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