QmlDesigner: Fill MouseArea to parent by default

Change-Id: I621fb57bf1c016c92b72a3d2271dd2f4af1e01eb
Reviewed-by: Marco Bubke <marco.bubke@qt.io>
(cherry picked from commit 09605ab4d7)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/plugins/qmldesigner/qtquickplugin/quick.metainfo

@@ -99,8 +99,7 @@ MetaInfo {
             libraryIcon: ":/qtquickplugin/images/mouse-area-icon.png"
             version: "2.0"
 
-            Property { name: "width"; type: "int"; value: 100; }
-            Property { name: "height"; type: "int"; value: 100; }
+            Property { name: "anchors.fill"; type: "enum"; value: parent; }
             toolTip: qsTr("An area with mouse functionality.")
         }
     }