Fix fading edge effect from impacting neighboring pixels

Bug: 132354626
Bug: 129117085
Test: skia unit tests and test cases described in the bug
Change-Id: Ieaa7c831dd6298ac0565e6f1837b1c1dbd4545da
(cherry picked from commit ac33a487516196e9f1cf830e78313806e6daf777)
9 files changed