QmlDesigner: Enable sourceRect property

Enable sourceRect property to Item layer specifics

Change-Id: If2f47c2ad47a083d5c4a30c9154a7631616ea257
Reviewed-by: Pranta Ghosh Dastider <pranta.dastider@qt.io>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

share/qtcreator/qmldesigner/propertyEditorQmlSources/QtQuick/LayerSection.qml

@@ -235,10 +235,10 @@ Section {
 
             ExpandingSpacer {}
         }
-/*
+
         PropertyLabel {
-            text: qsTr("Source Rectangle")
+            text: qsTr("Source rectangle")
-            tooltip: qsTr("TODO.")
+            tooltip: qsTr("Sets the rectangular area of the component that should be rendered into the texture.")
         }
 
         SecondColumnLayout {
@@ -313,6 +313,5 @@ Section {
 
             ExpandingSpacer {}
         }
-*/
     }
 }