appDisplay: Factor out function

The function to update the multiline state of the title label
will be reused by the next commit, so move it into a separate
method.

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1496

js/ui/appDisplay.js

@@ -1495,7 +1495,7 @@ class AppViewItem extends St.Button {
         }
     }
 
-    _onHover() {
+    _updateMultiline() {
         if (!this.icon.label)
             return;
 
@@ -1524,6 +1524,10 @@ class AppViewItem extends St.Button {
         });
     }
 
+    _onHover() {
+        this._updateMultiline();
+    }
+
     _onDragBegin() {
         this._dragging = true;
         this.scaleAndFade();