Move approx_acos and strided loads from GrVx to SkVx

Change-Id: Icf2d589b7a748f98cfa1be77217f5a21aed0a1b2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/457187
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
6 files changed