Add a16w8 per-op test for split (#19600) #5661

Job	Run time
test-coreml / test-backend-macos (coreml_static_int8, models) / macos-job	24m 36s
test-coreml / test-backend-macos (coreml, models) / macos-job	11m 59s
test-coreml / test-backend-macos (coreml, operators) / macos-job	10m 7s
test-coreml / test-backend-macos (coreml_static_int8, operators) / macos-job	2h 0m 44s
test-coreml / package-golden-artifacts	0s
test-coreml / test-backend-linux	-10s
	2h 47m 16s

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