skvx spring cleaning

  - remove some workarounds
  - more SI/SIN/SIT/SINT use
  - rewrap a lot of code to 100 cols
  - etc. misc.

Change-Id: I78b7ff272afcbb8658cf147aad8af85d0e2acf42
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/314676
Auto-Submit: Mike Klein <mtklein@google.com>
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Herb Derby <herb@google.com>

Author: Mike Klein