Implement log and log2 intrinsics in SkRP.

These already existed in Raster Pipeline, so they just needed to be
wired up into the SkRP builder and codegen. I also ported over the
SkVM unit test for log2 since we didn't have an RP equivalent.

Change-Id: Ida15486084ebd76f50f9aaa3c3c0e7d0c1b399f8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/658080
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
7 files changed