[applets/icon] Animate icon's opacity when fading out while busy
This is literally copied from PlasmaComponents.3/BusyIndicator.
To be merged after/together/instead of !2183 (merged) which is a clean up part of this MR.
This is literally copied from PlasmaComponents.3/BusyIndicator.
To be merged after/together/instead of !2183 (merged) which is a clean up part of this MR.