Introduce HLO graph bindings (#8564) #10746

Job	Run time
get-torch-commit	1s
Build PyTorch/XLA / build	32m 6s
Build docs / build-docs	1m 38s
TPU tests / tpu-test	46m 52s
CPU tests / test (benchmark_tests)	8m 41s
CPU tests / test (python_tests, xla_op1)	17m 43s
CPU tests / test (python_tests, xla_op2)	5m 38s
CPU tests / test (python_tests, xla_op3)	9m 9s
CPU tests / test (python_tests, torch_mp_op)	13m 10s
CPU tests / test (cpp_tests, cpp_tests1)	5m 37s
CPU tests / test (cpp_tests, cpp_tests2)	6m 1s
	2h 26m 36s

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