Add ceil to skvx/skvm/JIT, and floor/ceil intrinsics to ByteCode

This is enough to get the colorcube GM working on the CPU backend.
(It's not blazingly fast, but it works!)

Change-Id: Ic069861bab162ed49f876fd03af2cbaaec2da628
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/297718
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
8 files changed