Fix layout issues of Desktop Change OSD

* no more binding loops - yeah for anchoring
* properly update sizes when switching screens
* properly handle case layout indicator enabled/disabled
* connect to desktop changed and reset desktop model
* set a maximum width/height of 0.8 of screen

Most interesting change is the moving of
visible = true;
to the beginning of the block which updates the layout. Without that
all the changes are ignored resulting in the incorrect size on screen
change.

The disadvantage of that is that the OSD is shown before the layout is
adjusted. But it's considerable minor given that it should be just one
frame.




FIXED-IN: 4.10.1
REVIEW: 108945