Currently, Flutter redraws every pixel even if there's a very tiny part of the screen that's animating (e.g., CircularProgressIndicator, caret in TextField).

We should compute the damage rect (which shouldn't be hard due to our repaint mechanism), reuse the buffer from previous frames, and draw the new frame with the clip set to the damage rect.

Hopefully this could have a significant impact on CPU/GPU usages for issues like #31865