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
if (IDialogConstants.OK_LABEL.equals(buttonLabel)) {
			return IDialogConstants.OK_ID;
		}
    	
	    if (IDialogConstants.YES_LABEL.equals(buttonLabel)) {
			return IDialogConstants.YES_ID;
		}
	    
	    if (IDialogConstants.NO_LABEL.equals(buttonLabel)) {
			return IDialogConstants.NO_ID;
		}
	    
	    if (IDialogConstants.CANCEL_LABEL.equals(buttonLabel)) {
			return IDialogConstants.CANCEL_ID;
		}
	    
	    if (IDialogConstants.YES_TO_ALL_LABEL.equals(buttonLabel)) {
			return IDialogConstants.YES_TO_ALL_ID;
		}
	    
	    if (IDialogConstants.SKIP_LABEL.equals(buttonLabel)) {
			return IDialogConstants.SKIP_ID;
		}
	    
	    if (IDialogConstants.STOP_LABEL.equals(buttonLabel)) {
			return IDialogConstants.STOP_ID;
		}
	    
	    if (IDialogConstants.ABORT_LABEL.equals(buttonLabel)) {