add I16Vec and U16Vec (#439) #1048

Job	Run time
Lint	2m 9s
Test portable simd (ubuntu-latest, nightly)	43s
Test wasm (stable, ubuntu-latest)	4m 34s
Test portable simd (macos-latest, nightly)	1m 3s
Test portable simd (windows-latest, nightly)	1m 22s
Test (ubuntu-latest, stable)	3m 36s
Test (ubuntu-latest, beta)	2m 19s
Test (ubuntu-latest, nightly)	2m 20s
Test (macos-latest, stable)	5m 41s
Test (macos-latest, beta)	5m 0s
Test (macos-latest, nightly)	6m 52s
Test (windows-latest, stable)	4m 6s
Test (windows-latest, beta)	4m 4s
Test (windows-latest, nightly)	4m 8s
	47m 57s

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