QmlDesigner: Adding ExtendedFunction button to UrlChooser

This allows to edit/set bindings on urls for e.g. images.

Instead of the hack before we now use padding in the style
to reserve space for button.

Task-number: QTCREATORBUG-13328
Change-Id: I94bad70618440a2ed835629e561a394d76990883
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

share/qtcreator/qmldesigner/propertyEditorQmlSources/HelperWidgets/CustomComboBoxStyle.qml

@@ -33,6 +33,8 @@ ComboBoxStyle {
 
     }
 
+    padding.left: 20
+
     background: Item {
         implicitWidth: 120
         implicitHeight: 24
@@ -65,18 +67,14 @@ ComboBoxStyle {
         }
     }
 
-    label: Item {
-        implicitWidth: textitem.implicitWidth + 20
-        Text {
+    label: Text {
         id: textitem
         anchors.left: parent.left
-            anchors.leftMargin: 14
         anchors.verticalCenter: parent.verticalCenter
         text: control.currentText
         renderType: Text.NativeRendering
         color: control.textColor
     }
-    }
 
     __dropDownStyle: MenuStyle {
         __maxPopupHeight: 600

share/qtcreator/qmldesigner/propertyEditorQmlSources/HelperWidgets/UrlChooser.qml

@@ -52,6 +52,13 @@ RowLayout {
     Controls.ComboBox {
         id: comboBox
 
+        ExtendedFunctionButton {
+            x: 2
+            anchors.verticalCenter: parent.verticalCenter
+            backendValue: urlChooser.backendValue
+            visible: comboBox.enabled
+        }
+
         property bool isComplete: false
 
         function setCurrentText(text) {