Bug 273330 [JFace] Add API to MessageDialog to enable clients to use SWT.SHEET
A new style constant SWT.SHEET was added recently. Without adding new API in JFace, clients who are currently using the convenience methods MessageDialog.openWarning/Error/Information/Question/Confirmation would not be able to open these dialogs as sheets.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/MessageDialogWithToggle.java
/**
     * An accessor for the current preference store for this dialog.
     * 
     * @return The preference store; this value may be <code>null</code> if no
     *         preference is being used.
     */
    public IPreferenceStore getPrefStore() {
        return prefStore;
    }
    /**
     * An accessor for the current key of the toggle preference.
     * 
     * @return The preference key; this value may be <code>null</code> if no
     *         preference is being used.
     */
    public String getPrefKey() {
        return prefKey;
    }
    /**
     * Returns the toggle state. This can be called even after the dialog is
     * closed.
     * 
     * @return <code>true</code> if the toggle button is checked,
     *         <code>false</code> if not
     */
    public boolean getToggleState() {
        return toggleState;
    }
    /**
     * A mutator for the key of the preference to be modified by the toggle