Update emitter code and documentation naming

[JialinHuang803]

Since cadl has been renamed to TypeSpec, we should update the code and filenames to remove any references to "cadl-ranch".

[MaryGao]

I think it is time to refine our document naming things with RLC/HLC/Modular. Jose has a proposal that we could reference.

[qiaozha]

Please consider update the docs in azure-sdk-for-js repo and the typespec-azure repo and the codegen repo.