Bind clones opacity to the window actors opacity
During workspace animation and other actions we are creating clones, but they are designed to have full opacity and not to follow the cloned actor opacity even if the source actor use different opacity levels.
This implies that if something (e.g. an extension) changes sets a window opacity to a different level, we don't respect that during the workspace animation.
So, let's just bind the opacity property to the clone during the animation. There's no need to manually unbind it since we always destroy the clone explicitly, breaking the bind.
As per the analysis done in !3285 (comment 2093991) basically in the current state the opacity is not bound leading to being reset to default:
Apply the same also to the windowsThumbnails as it seems a place where it should