* Revert "docs for image disposal (#67066)"
This reverts commit bcb2ac5a55.
* Revert "Dispose of images after using them (#66688)"
This reverts commit a7954691da.
* Dispose of images after using them
Adds ImageInfo.clone, ImageInfo.dispose, and ImageInfo.isCloneOf.
Makes all stateful holders of ui.Image objects properly clone and dispose of them.
Behavior change for ImageStreamCompleter: Removing the last listener after registering at least one listener results in the object being disposed, and new listeners cannot be added, unless a keepAlive handle is created.
Makes all non-stateful holders of ui.Image (i.e. paintImage and RawImage) assert that whoever gave the image to them has not disposed it on them.
