reproduction steps

see #148496

observed results

(notice the purple exclamations in the workload to the left)

expected results

I would expect these textures to be reused across frames, and/or reused for the one frame if that's possible with the correct synchronization.

notes

Jonah said that we do this sort of caching for save layers (https://github.com/flutter/engine/blob/main/impeller/entity/render_target_cache.h).