Add a16w8 per-op test for bmm #5644

Job	Run time
test-coreml / test-backend-macos (coreml, operators) / macos-job	8m 44s
test-coreml / test-backend-macos (coreml, models) / macos-job	8m 43s
test-coreml / test-backend-linux	-1s
test-coreml / package-golden-artifacts	-1s
	17m 25s

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