TextArea: allow declaring child elements inline

Change-Id: I7da8e3664d6bd3ee9a8c4f22d4a5b686d1c5b5a9
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>

src/controls/TextArea.qml

@@ -608,6 +608,9 @@ ScrollView {
     */
     property alias backgroundColor: colorRect.color
 
+    /*! \internal */
+    default property alias data: area.data
+
     /*! \internal */
     property int __documentMargin: 4