Fix ConcurrentModifcationException in MenuObjectEditPart

The edit-part registry of a viewer might change when refreshing an
edit-part. To avoid this, use a copy of all edit-parts.

Seen in MenuComplexTest.test_CREATE_popup_newItem_deep

Author: ptziegler

org.eclipse.wb.core/src/org/eclipse/wb/internal/core/gef/part/menu/MenuObjectEditPart.java

@@ -205,7 +205,7 @@ public EditPart getTargetEditPart(Request request) {
 				public void run() {
 					try {
 						MenuObjectInfoUtils.m_selectingObject = m_object;
-						for (EditPart editPart : getViewer().getEditPartRegistry().values()) {
+						for (EditPart editPart : List.copyOf(getViewer().getEditPartRegistry().values())) {
 							if (editPart instanceof MenuObjectEditPart) {
 								editPart.refresh();
 							}