appDisplay: Animate DnD app icons at the position they were dropped

We currently don't indicate whether dropping an app icon was successful
or not, let's do that by using the zoom out animation of the app icon
and show that animation at the position the drop happened.

GNOME/gnome-shell!121
4 jobs for !121 with dash-fixes in 14 minutes and 42 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Review
passed #352735
check_commit_log

00:00:22

 
  Build
passed #352736
build

00:11:51

 
  Test
passed #352737
test

00:02:27

passed #352738
test-pot

00:02:24