fill in most remaining skvx operations

Obviously lots of these new operations like sqrt() will want platform
specialization.  That'll come later.

Change-Id: Ia0758425d4ec5911968a3d0ad63fa387b9b4cb39
Reviewed-on: https://skia-review.googlesource.com/c/189848
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
2 files changed