effects/desktopgrid: Replace highly opmitized animators with animations which work

Unfortunately, *Animator QML types have some problems with rendering,
sometimes affecting general smoothness, other times (like here, for me)
just not animating entirely. On my NVIDIA graphics system the animation
or a desktop returning from drag just looks like a freeze for a second,
then it suddenly jumps back to {0,0}. So let's just replace with less
optimal NumberAnimation which works fine.

FIXED-IN: 5.26

src/effects/desktopgrid/qml/DesktopView.qml

@@ -145,7 +145,7 @@ FocusScope {
         }
         Behavior on x {
             enabled: !dragHandler.active
-            XAnimator {
+            NumberAnimation {
                 id: xAnim
                 duration: container.effect.animationDuration
                 easing.type: Easing.OutCubic
@@ -153,7 +153,7 @@ FocusScope {
         }
         Behavior on y {
             enabled: !dragHandler.active
-            YAnimator {
+            NumberAnimation {
                 id: yAnim
                 duration: container.effect.animationDuration
                 easing.type: Easing.OutCubic