Adds the SDL_EVENT_WINDOW_OCCLUDED events and the window flag SDL_WINDOW_OCCLUDED to report when the window occlusion state has changed, so that the application can take appropriate measures, as it may wish to suspend drawing, throttle, or otherwise behave in a more energy efficient manner when the window is not visible. When the window is no longer occluded, the SDL_EVENT_WINDOW_EXPOSED event is sent and the occlusion flag is cleared.
This is handled on macOS via the window occlusion state event (available as of 10.9), and via the xdg-shell protocol on Wayland (version 6, wayland-protocols 1.32, passed through in libdecor 0.1.2).
Now you don't need the latest Wayland installed to build with
newer protocols supported, as they'll build correctly; even if
your system can't use them, we can make intelligent decisions
at runtime about what's available on the current machine anyhow.
This also simplifies some logic and possible failure cases in
the configure and CMake scripts.
Fixes Bugzilla #4207.
Frank Praznik