7bd544a79c
Fixes https://github.com/flutter/flutter/issues/105071. Lets use switches instead of maps. First, they don't encounter runtime constructors. Second, they will yell at static analysis if there is a missing case (as long as we don't have `default`s). Also fixed a Metal validation issue. Since we weren't sampling from the source in case of a foreground, we weren't binding a texture and sampler at that location. I just bound the dest to that spot and everyone is happy. We won't actually sample from that binding.