Merge "[RenderEngine] correct alpha blending func" am: 6f94260396 am: 9592c9d586 am: d0567ad4a1 am: 444c983529

Original change: https://android-review.googlesource.com/c/platform/frameworks/native/+/1391116

Change-Id: I59f1be5a6465fc64012c45e7dd1dec7eea8e647e