Run lazy tensor codegen in generate_code.py (#73996)
Summary:
Hooks into existing autograd codegen script (generate_code.py) to take advantage of its integrations into buck/cmake/bazel.
Adds a new option (--gen_lazy_ts_backend) to. generate_code.py, calling this from CMake OSS build and fbcode build, but not from other internal xplat/ovrsource builds (these could be opted in later)
Bazel support is added in a later diff.
Includes one generated file (torch/csrc/lazy/generated/LazyIr.h) in a unit test (test/cpp/lazy/test_ir.cpp) to partially verify the generator is working, but does not compile the remaining output sources from the generator yet as they depend on other files not yet landed from lazy_tensor_staging branch.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/73996
Test Plan: OSS/internal CI - verify all builds are working and test_ir.cpp compiles LazyIr.h
Reviewed By: ezyang
Differential Revision: D34408536
fbshipit-source-id: 8af0aea3b95d81eccafc17d64390d70ddd176515
(cherry picked from commit f930612f2bad61c76eb02d85cfbec9f33a1459dc)
