Make codegen backend agnostic minus fallbacks (#2944)
* use in-tree public codegen API.
* use in-tree public codegen API.
* use in-tree public codegen API.
* stop pinning to feature branch
* remove torch_pin file before merging. preemptively update yaml to incorporate #2891
* use in-tree public codegen API.
* stop pinning to feature branch
* [WIP] remove bridge:: api from codegen. Start auto-gen'ing out/inplace kernels when possible
* updated torch pin
* fix missing ops in yaml
* remove torch_pin file before merging. preemptively update yaml to incorporate #2891
* make codegen backend-agnostic, except for CPU fallbacks
* remove logging
* fix straggler AtenXlaType ops
* lint
* rename aten_xla_type.h -> XLANativeFunctions.h
* rename aten_xla_type.h -> XLANativeFunctions.h
* fix rename, delete aten_xla_type.h
* update torch_pin after the file rename
* remove logging info from yaml
* lint
* doc fix
* rebase fix
* remove torch pin
