Add CoreML-stable RMSNorm for llama eager paths (#19523) (#19523) #5392

Job	Run time
test-arm / test-backend-linux (arm_vgf_fp, models) / linux-job	20m 2s
test-arm / test-backend-linux (arm_tosa_fp, operators) / linux-job	23m 42s
test-arm / test-backend-linux (arm_vgf_fp, operators) / linux-job	25m 31s
test-arm / test-backend-linux (arm_tosa_fp, models) / linux-job	18m 20s
test-arm / test-backend-macos	0s
test-arm / package-golden-artifacts	42s
	1h 28m 17s

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