effects/windowview: Fix "Unable to assign [undefined] to int"

animationDuration is not defined in WindowViewEffect. Use
heap.animationDuration instead.

src/effects/private/qml/WindowHeap.qml

@@ -73,7 +73,7 @@ FocusScope {
                 component TweenBehavior : Behavior {
                     enabled: thumb.state !== "partial" && heap.animationEnabled && !thumb.activeDragHandler.active
                     NumberAnimation {
-                        duration: effect.animationDuration
+                        duration: heap.animationDuration
                         easing.type: Easing.OutCubic
                     }
                 }
@@ -121,7 +121,7 @@ FocusScope {
                         to: "normal"
                         enabled: heap.animationEnabled
                         NumberAnimation {
-                            duration: effect.animationDuration
+                            duration: heap.animationDuration
                             properties: "x, y, width, height, opacity"
                             easing.type: Easing.OutCubic
                         }

src/effects/windowview/qml/main.qml

@@ -42,7 +42,7 @@ Item {
         layer.effect: FastBlur {
             radius: container.organized ? 64 : 0
             Behavior on radius {
-                NumberAnimation { duration: effect.animationDuration; easing.type: Easing.OutCubic }
+                NumberAnimation { duration: container.animationDuration; easing.type: Easing.OutCubic }
             }
         }
     }