Fix active value field detection for value fields containing a widget

The method _getActiveValueField can not detect the active value field
for value fields that include a widget (e.g. a value field containing a
code editor widget), because the contained widget is not a value field
itself.

As a solution for this kind of fields look for the parents as well.

eclipse-scout-core/src/form/fields/ValueField.ts

@@ -678,10 +678,11 @@ export class ValueField<TValue extends TModelValue, TModelValue = TValue> extend
   protected static _getActiveValueField(target: Element): ValueField<any> {
     let $activeElement = $(target).activeElement(),
       activeWidget = scout.widget($activeElement);
-    if (activeWidget instanceof ValueField && activeWidget.enabledComputed) {
-      return activeWidget;
+    if (activeWidget instanceof ValueField) {
+      return activeWidget.enabledComputed ? activeWidget : null;
     }
-    return null;
+    const parent = activeWidget && activeWidget.findParent(parent => parent instanceof ValueField) as ValueField<any>;
+    return (parent && parent.enabledComputed) ? parent : null;
   }
 }