Hide ExpandableNode from client's label provider.

Unsafe(No type check before accessing passed model element) client's
label provider can lead to ClassCastException. So we can never pass
ExpandableNode to client's label provider.

see eclipse-platform#1353

bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerColumn.java

@@ -138,17 +138,16 @@ public void setEditingSupport(EditingSupport editingSupport) {
 			Assert.isTrue(false, "Column " + cell.getColumnIndex() + //$NON-NLS-1$
 			" has no label provider."); //$NON-NLS-1$
 		}
-		labelProvider.update(cell);
-
-		// check if client has updated the label for this element. Otherwise use default
-		// label provided
+		// Set font and label for ExpandableNode. Client label provider should not
+		// receive it.
 		if (cell.getElement() instanceof ExpandableNode expNode) {
 			cell.setFont(JFaceResources.getFontRegistry().getItalic(JFaceResources.DEFAULT_FONT));
-			String text = cell.getText();
-			if (text.isEmpty() || text.equals(expNode.toString())) {
-				cell.setText(expNode.getLabel());
-			}
+			cell.setText(expNode.getLabel());
+			return;
 		}
+
+		labelProvider.update(cell);
+
 	}
 
 	/**