Add a16w8 per-op test for split #5317

Job	Run time
test-arm / test-backend-linux (arm_tosa_fp, operators) / linux-job	1m 41s
test-arm / test-backend-linux (arm_tosa_fp, models) / linux-job	1m 40s
test-arm / test-backend-linux (arm_vgf_fp, models) / linux-job	1m 36s
test-arm / test-backend-linux (arm_vgf_fp, operators) / linux-job	1m 45s
test-arm / test-backend-macos	-1s
test-arm / package-golden-artifacts	0s
	6m 41s

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