Issue #11251: Fixes edit->clear by refreshing the selected drawables
Both clear and undo functions now refresh the drawable, and the filters inside it. I figured while testing that toggling the layer effect off and on used to get rid of the remaining pixels, so I made some functions to do that. I am not sure, but maybe we could fix other issues related to effects like this too, by refreshing the drawables?
I have tested undo, redo, and using clicking to traverse the undo stack in the test below.