layernorm support #5679

Job	Run time
apple (aarch64-apple-ios)	1m 57s
apple (aarch64-apple-darwin)	4m 41s
linux (raspbian)	8m 3s
linux (aarch64-unknown-linux-gnu)	11m 57s
linux (armv6vfp-unknown-linux-gnueabihf)	10m 15s
linux (armv7-unknown-linux-gnueabihf)	10m 52s
linux (aarch64-unknown-linux-musl)	12m 30s
linux (armv7-unknown-linux-musl)	10m 14s
linux (aarch64-linux-android)	1m 28s
linux (armv7-linux-androideabi)	1m 26s
linux (i686-linux-android)	3m 53s
linux (x86_64-linux-android)	1m 16s
linux (wasm32-unknown-unknown)	33s
linux (wasm32-wasi)	30s
	1h 19m 35s

Provide feedback