Metal backend: Add gather_qmv kernel for MoE expert-indexed quantized… #2969

Job	Run time
test-arm / test-backend-linux (arm_tosa_fp, operators) / linux-job	18m 48s
test-arm / test-backend-linux (arm_ethos_u85, models) / linux-job	40m 5s
test-arm / test-backend-linux (arm_tosa_int, models) / linux-job	36m 29s
test-arm / test-backend-linux (arm_ethos_u55, models) / linux-job	43m 41s
test-arm / test-backend-linux (arm_vgf_fp, models) / linux-job	31m 44s
test-arm / test-backend-linux (arm_ethos_u55, operators) / linux-job	33m 49s
test-arm / test-backend-linux (arm_vgf_int, operators) / linux-job	29m 0s
test-arm / test-backend-linux (arm_vgf_fp, operators) / linux-job	16m 26s
test-arm / test-backend-linux (arm_tosa_int, operators) / linux-job	30m 29s
test-arm / test-backend-linux (arm_tosa_fp, models) / linux-job	31m 18s
test-arm / test-backend-linux (arm_vgf_int, models) / linux-job	38m 38s
test-arm / test-backend-linux (arm_ethos_u85, operators) / linux-job	32m 18s
test-arm / test-backend-macos	-1s
test-arm / package-golden-artifacts	49s
	6h 23m 33s

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