Window decorations: support toolbox-style "small" window title bar

[DevCharly]

This PR adds support for toolbox-style "small" window title bars if FlatLaf Window decorations are used.
See issue #659

The "small" window title bar has a smaller height, smaller iconify/maximize/close buttons and the font of the title is also smaller:

Default window title bar for comparison:

To enable small title bar either set window type to utility:

frame.setType( Window.Type.UTILITY );

Or set client property on root pane:

frame.getRootPane().putClientProperty( "Window.style", "small" );

This is compatible to Java on macOS, which supports small title bar out of the box. See screenshot here #659