[NFC][HLSL][RootSignature] Split up `HLSLRootSignatureUtils`

[inbelic]

Utils files tend to generally end up as a dumping grounds of many different parts.

This issue track the non-functional change to move the metadata related logic into RootSignatureMetadata and the serialization logic into RootSignature.

AC:

• Remove the RootSignatureUtils library
• Move metadata logic into the RootSignatureMetadata library
• Move serialization logic into the HLSLRootSignature library