Cleanup unnecessary null comparison before instanceof check in java.desktop

Update code checks both non-null and instance of a class in java.desktopmodule classes.
The checks and explicit casts could also be replaced with pattern matching for the instanceof operator.
For example the following code:

        if (parent != null) {
            if (parent instanceof ScreenMenu) {
                final ScreenMenu sm = (ScreenMenu)parent;
                sm.setChildVisible(fInvoker, b);
            }
        }


Can be simplified to:
    
        if (parent instanceof ScreenMenu sm) {
            sm.setChildVisible(fInvoker, b);
        }