appDisplay: Add API to animate launch at given position

Add a `animateLaunchAtPos()` method to the AppIcon class to animate the
launch of an app at a given position. This allows for a visual
indication of whether dropping an app icon using DnD was successful at
the position the drop happened in a later commit.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/121

js/ui/appDisplay.js

@@ -2208,6 +2208,10 @@ var AppIcon = class AppIcon {
         this.icon.animateZoomOut();
     }
 
+    animateLaunchAtPos(x, y) {
+        this.icon.animateZoomOutAtPos(x, y);
+    }
+
     scaleIn() {
         this.actor.scale_x = 0;
         this.actor.scale_y = 0;