[NFC][HLSL][DirectX] Move validations from `DXILRootSignature` pass to `Frontend/HLSL/RootSignature`

[inbelic]

This issue tracks a non-functional change to move all, currently static, validations functions into a common interface in Fronted/HLSL/RootSignature.

This will allow the re-use of these verification functions for #129940.

AC:

• Extend HLSLRootSignature.[h|cpp] to provide an interface for the basic validations of root signatures
• DXILRootSignature should be updated to depend on Frontend/HLSL/RootSignature and use the validation interface provided there