Add MLX support for draft model #810

Job	Run time
test-webgpu / test-backend-linux (webgpu, models) / linux-job	17m 3s
test-webgpu / test-backend-linux (webgpu, operators) / linux-job	39m 33s
test-webgpu / test-backend-macos	-7s
test-webgpu / package-golden-artifacts	1m 31s
	58m 0s

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