[Impeller] Engine gets confused when enable_impeller and enable_software_rendering are both true. #127500
Description
Steps:
Create an app that displays an image.
Open a simulator.
Run flutter run --enable-software rendering.
The image will fail to render.
This has the same root cause as #126768 (comment)
IMHO we need the following:
- Better runtime behavior when enable_impeller is true but impeller can't/won't be enabled (because no valid MTLDevice is available or because the user explicitly requested software rendering).
- Better behavior in the tool when a user requests both impeller (implicitly or explicitly) and software rendering (explicitly).