Adds Uint32x4, Uint16x8, and Uint8x16 types.
Adds all functions in the current spec, except for loads and stores.

LOG=Y
BUG=v8:4124

Committed: https://crrev.com/4be6d37fd1ad0a6e0ea37da8863ae5169c2b89ba
Cr-Commit-Position: refs/heads/master@{#30322}

Review URL: https://codereview.chromium.org/1294513004

Cr-Commit-Position: refs/heads/master@{#30353}