Add CoreML-stable RMSNorm for llama eager paths (#19523) (#19523) #5393

Job	Run time
test-arm / test-backend-linux (arm_tosa_fp, models) / linux-job	18m 41s
test-arm / test-backend-linux (arm_vgf_fp, models) / linux-job	19m 2s
test-arm / test-backend-linux (arm_tosa_fp, operators) / linux-job	22m 17s
test-arm / test-backend-linux (arm_vgf_fp, operators) / linux-job	25m 2s
test-arm / test-backend-macos	-10s
test-arm / package-golden-artifacts	42s
	1h 25m 34s

Provide feedback