Jonah Williams 26d612bbf4 [impeller] premultiply vertices colors. (flutter/engine#45406) ...

Lost this after the transition.

### After

![image](https://github.com/flutter/engine/assets/8975114/cec40045-581a-4bc4-8470-fbc201a0773b)

### Before

![image](https://github.com/flutter/engine/assets/8975114/23229175-54db-4aac-8605-cfe8568be436)

2023-09-02 00:18:05 +00:00

..

src/flutter

[impeller] premultiply vertices colors. (flutter/engine#45406)

2023-09-02 00:18:05 +00:00