Bug 58777 [Viewers] add API to not deactivate CellEditor on FocusLost
TableViewerImpl installs a FocusListener on CellEditors, which calls applyEditorValue() on focusLost events. This FocusListener must be removed since applying the editor value is not always the wanted behavior on focusLost. Subclasses of CellEditor already handle focus loss in an extensible way: they install their own FocusListener and call a hook method focusLost() (which can be extended or reimplemented by subclasses with special needs). To support content assist in table cells (such as in the Change Method Signature dialog), we need to stay in editing mode even while the proposal list has focus. This is currently not implementable, since TableViewerImpl deactivates the CellEditor even if the CellEditor's focusLost() is reimplemented. The fix is to simply remove the redundant FocusListener in TableViewerImpl.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/CellEditor.java
* Processes a key release event that occurred in this cell editor.
     * <p>
     * The default implementation of this framework method cancels editing
     * when the ESC key is pressed.  When the RETURN key is pressed the current
     * value is applied and the cell editor deactivates.
     * Subclasses should call this method at appropriate times. 
     * Subclasses may also extend or reimplement.
     * </p>
     *
     * @param keyEvent the key event
     */
    protected void keyReleaseOccured(KeyEvent keyEvent) {
        if (keyEvent.character == '\u001b') { 
            fireCancelEditor();
        } else if (keyEvent.character == '\r') { 
            fireApplyEditorValue();
            deactivate();
        }
    }
    /**
     * Processes a focus lost event that occurred in this cell editor.
     * <p>
     * The default implementation of this framework method applies the current
     * value and deactivates the cell editor.
     * Subclasses should call this method at appropriate times. 
     * Subclasses may also extend or reimplement.
     * </p>
     */
    protected void focusLost() {
        if (isActivated()) {