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/MessageDialog.java
/**
     * Constant for a dialog with no image (value 0).
     */
    public final static int NONE = 0;
    /**
     * Constant for a dialog with an error image (value 1).
     */
    public final static int ERROR = 1;
    /**
     * Constant for a dialog with an info image (value 2).
     */
    public final static int INFORMATION = 2;
    /**
     * Constant for a dialog with a question image (value 3).
     */
    public final static int QUESTION = 3;
    /**
     * Constant for a dialog with a warning image (value 4).