QmlDesigner: Fix property panes top part layout

Search bar was not visible at all and texture pane had weird order
with preview above toolbars.

Change-Id: I13d0c5383919ba79e54d3fb4a754d9091a7a480c
Reviewed-by: Ali Kianian <ali.kianian@qt.io>

share/qtcreator/qmldesigner/propertyEditorQmlSources/QtQuick3D/TexturePane.qml

@@ -34,16 +34,14 @@ Rectangle {
             Layout.fillWidth: true
         }
 
-        Texture.TopSection {
-            id: topSection
-
-            Layout.fillWidth: true
-        }
-
         PropertyEditorPane {
             Layout.fillWidth: true
             Layout.fillHeight: true
 
+            headerComponent: Texture.TopSection {
+                id: topSection
+            }
+
             DynamicPropertiesSection {
                 propertiesModel: PropertyEditorDynamicPropertiesModel {}
                 visible: !hasMultiSelection

share/qtcreator/qmldesigner/propertyEditorQmlSources/imports/HelperWidgets/PropertyEditorPane.qml

@@ -39,6 +39,7 @@ Rectangle {
         id: propertySearchBar
 
         contentItem: mainColumn
+        anchors.top: itemPane.top
         width: parent.width
         z: parent.z + 1
     }
@@ -73,6 +74,7 @@ Rectangle {
 
     Rectangle {
         id: stateSection
+        anchors.top: toolbar.bottom
         width: itemPane.width
         height: StudioTheme.Values.height + StudioTheme.Values.controlGap * 2
         color:  StudioTheme.Values.themePanelBackground