TransformUI causes flickering

[weisJ]

When running with java >= 16 we can't rely on setting a delegate repaint manager as the method to do so resides in SwingUtilities3 which isn't exported by the jdk as a module. Instead we need to wrap the global RepaintManager, which causes us to loose buffering information (and capability) resulting in flickering while resizing.

To stay compliant with module restrictions the fallback method is the standard for java >= 16 with the option to opt-in to the better approach by setting darklaf.useBufferedRepaintManage to true in the system properties and starting the application with
--add-exports java.desktop/com.sun.java.swing=ALL-UNNAMED (once #246 is merged this will be --add-exports java.desktop/com.sun.java.swing=darlaf.core)

Ideally we should find a better way to handle repaints in the TransformUI, which supports buffering without relying on internal API.