[HLSL] Implement serialization of a root signature declaration

[inbelic]

This issue tracks implementation of a text serialization for the in-memory representation of a root signature to be displayed when dumping a RootSignatureDecl as introduced for #119011.

This issue is ready to move out of planning when it is determined if we should implement such a serialization (will it be useful for testing purposes and/or if it would be valuable for a user to be able to see the construct root signature memory when dumping the AST decl).

AC:

• All sub-issues are completed
• TextNodeDumper::VisitHLSLRootSignatureDecl is defined to dump the serialized text

[inbelic]

From design meeting: go about the approach of just naively dumping all the in-memory information to start, and we can see how the verbosity helps/impedes to determine if we want to add complexity to tracking which params were explicitly denoted, etc.