Bug 201906 [Viewers] 3.4 ColumnViewerEditor leaks ViewerCell instances.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ColumnViewerEditor.java
&& !editorActivationListener.isEmpty()) {
					Object[] ls = editorActivationListener.getListeners();
					for (int i = 0; i < ls.length; i++) {
						((ColumnViewerEditorActivationListener) ls[i])
								.beforeEditorActivated(activationEvent);
						
						if (activationEvent.cancel) {
							return;
						}
					}
				}
				updateFocusCell(cell, activationEvent);
				cellEditor.addListener(cellEditorListener);
				part.getEditingSupport().initializeCellEditorValue(cellEditor,
						cell);
				
				
				
				
				
				final Control control = cellEditor.getControl();
				cellEditor.activate(activationEvent);
				if (control == null) {
					return;
				}
				setLayoutData(cellEditor.getLayoutData());
				setEditor(control, (Item) cell.getItem(), cell.getColumnIndex());
				cellEditor.setFocus();
				if (cellEditor.dependsOnExternalFocusListener()) {
					if (focusListener == null) {