Add dlpack support #8214

Job	Run time
Build XLA CUDA plugin / build	5m 10s
Build PyTorch/XLA / build	31m 32s
TPU tests	0s
GPU tests / test (benchmark_tests)	5m 26s
GPU tests / test (python_tests, xla_op1)	30m 4s
GPU tests / test (python_tests, xla_op2)	5m 7s
Build docs / build-docs	1m 57s
GPU tests / test (python_tests, xla_op3)	39m 59s
GPU tests / test (python_tests, torch_mp_op)	47m 1s
CPU tests / test (benchmark_tests)	2m 4s
GPU tests / test (cpp_tests, cpp_tests1)	7m 50s
CPU tests / test (python_tests, xla_op1)	10m 52s
GPU tests / test (cpp_tests, cpp_tests2)	15m 26s
CPU tests / test (python_tests, xla_op2)	1m 47s
CPU tests / test (python_tests, xla_op3)	4m 1s
CPU tests / test (python_tests, torch_mp_op)	14m 53s
CPU tests / test (cpp_tests, cpp_tests1)	2m 58s
CPU tests / test (cpp_tests, cpp_tests2)	2m 54s
	3h 49m 1s

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