[Impeller] Fix modulate blend mode #36659
Merged
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Before, modulate was just clearing out the pass due to the zero alpha factors. The color is
src * dst
, which is correct. This patch sets the alpha to also besrc * dst
.Skia on left, Impeller on right:
![Screen Shot 2022-10-07 at 4 45 09 AM](https://user-images.githubusercontent.com/919017/194545714-bc0ac139-a1e0-4d3c-9a42-fedcf3ee16a5.png)