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
* Optional cell editor validator; <code>null</code> if none.
     */
    private ICellEditorValidator validator = null;
    /**
     * The error message string to display for invalid values;
     * <code>null</code> if none (that is, the value is valid).
     */
    private String errorMessage = null;
    /**
     * Indicates whether this cell editor has been changed recently.
     */
    private boolean dirty = false;
    /**
     * This cell editor's control, or <code>null</code>
     * if not created yet.
     */
    private Control control = null;
    /**
     * Default cell editor style
     */
    private static final int defaultStyle = SWT.NONE;
    /**
     * This cell editor's style
     */
    private int style = defaultStyle;
    /** 
     * Struct-like layout data for cell editors, with reasonable defaults
     * for all fields.
     */
    public static class LayoutData {