- Eliminates b1x4, b1x8, and b1x16 as distinct WASM types.
- All vector comparisons return v128 type.
- Eliminates b1xN and, or, xor, not.
- Selects take a v128 mask vector and are now bit-wise.
- Adds a new test for Select, where mask is non-canonical (not 0's and -1's).

LOG=N
BUG=v8:6020

Review-Url: https://codereview.chromium.org/2919203002
Cr-Commit-Position: refs/heads/master@{#45795}