Add the ability to import and wrap external surfaces from external toolkits such as Qt and GTK.
Wayland surfaces and windows are more intrinsically tied to the client library than other windowing systems, so it is necessary to provide a way to initialize SDL with an existing wl_display object, which needs to be set prior to video system initialization, or export the internal SDL wl_display object for use by external applications or toolkits. For this, the global property SDL_PROPERTY_GLOBAL_VIDEO_WAYLAND_WL_DISPLAY_POINTER is used.
A Wayland example was added to testnative, and a basic example of Qt 6 interoperation is provided in the Wayland readme to demonstrate the use of external windows with both SDL owning the wl_display, and an external toolkit owning it.
Sam Lantinga