- Adds support for modal windows to Win32, Mac, and Haiku, and enhances functionality on Wayland and X11, which previous set only the parent window, but not the modal state.
- Windows can be declared modal at creation time, and the modal state can be toggled at any time via SDL_SetWindowModalFor() (tested with UE5 through sdl2-compat).
- Allows dynamic unparenting/reparenting of windows.
- Includes a modal window test.