Implement Sk2f::Store4

Bug: skia:
Change-Id: I2adb983d68625d327e7c00e53b6ae4703b46252f
Reviewed-on: https://skia-review.googlesource.com/104761
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
3 files changed