add support for Apple Metal #3149

Job	Run time
pjrt-darwin-aarch64	7s
pjrt-darwin-aarch64	7s
pjrt-linux-x86_64	6s
pjrt-linux-x86_64	6s
pjrt-plugin-xla-cpu-darwin-aarch64	12s
pjrt-plugin-xla-cpu-darwin-aarch64	12s
pjrt-plugin-xla-cpu-linux-x86_64	11s
pjrt-plugin-xla-cpu-linux-x86_64	11s
build-tests-apple-metal	14m 42s
build-tests-apple-metal	14m 42s
build-tests-xla-cpu-darwin-aarch64	15m 47s
build-tests-xla-cpu-darwin-aarch64	15m 47s
build-tests-xla-cpu-linux-x86_64	2m 12s
build-tests-xla-cpu-linux-x86_64	2m 12s
build-tests-xla-cuda-linux-x86_64	3m 0s
build-tests-xla-cuda-linux-x86_64	3m 0s
pjrt-plugin-apple-metal	7s
pjrt-plugin-apple-metal	7s
pjrt-plugin-xla-cuda-linux-x86_64	11s
pjrt-plugin-xla-cuda-linux-x86_64	11s
readme	1m 3s
readme	1m 3s
shellcheck	5s
shellcheck	5s
tutorials	54s
tutorials	54s
test-xla-cpu-linux-x86_64	1m 32s
test-xla-cpu-linux-x86_64	1m 16s
test-xla-cuda-linux-x86_64	1m 15s
test-xla-cuda-linux-x86_64	1m 15s
test-apple-metal	13s
test-apple-metal	11s
test-xla-cpu-darwin-aarch64	3m 5s
test-xla-cpu-darwin-aarch64	3m 5s
	1h 29m 6s

Provide feedback