QtQuick.tooling: Add isRequired to Property

Previously parsing qmltypes with qml would fail due to this.

Change-Id: Ib5498eb75cbb6873cc5d4e8c798baefa1204bd8a
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/imports/tooling/Property.qml

@@ -43,6 +43,7 @@ Member {
     required property string type
     property bool isPointer: false
     property bool isReadonly: false
+    property bool isRequired: false
     property bool isList: false
     property int revision: 0
     property string bindable