[HLSL] Implement Root Signature Parsing of Root Parameters

[inbelic]

This issues handles defining RootCBV, RootSRV and RootUAV in-memory representation and the extra keyword/enum tokens required for lexing. Then we implement a ParseRootParameters method to construct the struct using previously defined parse methods.

Dependent on #126569

AC:

• Define the required keyword/enums for the Lexer
• Define the parsing method
• Define the in-memory representation of RootCBV, RootSRV and RootUAV
• Add additional unit testing