use in-tree public codegen API. (#2898)
* use in-tree public codegen API.
* use in-tree public codegen API.
* use in-tree public codegen API.
* use in-tree public codegen API.
* updated the docs to mention new codegen
* stop pinning to feature branch
* remove torch_pin file before merging. preemptively update yaml to incorporate #2891
* update list of ops to be in sync with master
* add clamp ops to xla_native_functions.yaml
