effects/overview: Disable animations until started

Once an animation starts due to property change, it cannot be easily
re-targeted. This can cause undesired animation jumps if a property
changes during startup (for example from 0 to its final value).

With this change, the window heap's animation will be disabled until
the effect starts the intro animation.

src/effects/overview/qml/ScreenView.qml

@@ -13,9 +13,11 @@ FocusScope {
     id: container
     focus: true
 
+    property bool animationEnabled: false
     property bool organized: false
 
     function start() {
+        container.animationEnabled = true;
         container.organized = true;
     }
 
@@ -84,6 +86,7 @@ FocusScope {
         width: heapArea.width
         height: heapArea.height
         focus: true
+        animationEnabled: container.animationEnabled
         organized: container.organized
         model: KWinComponents.ClientFilterModel {
             activity: KWinComponents.Workspace.currentActivity

src/effects/overview/qml/WindowHeap.qml

@@ -23,6 +23,8 @@ FocusScope {
 
     property alias model: windowsRepeater.model
     property int selectedIndex: -1
+    property bool animationEnabled: false
+
     required property bool organized
 
     ExpoLayout {
@@ -99,6 +101,7 @@ FocusScope {
                 ]
 
                 component TweenBehavior : Behavior {
+                    enabled: heap.animationEnabled
                     NumberAnimation {
                         duration: effect.animationDuration
                         easing.type: Easing.InOutCubic