This fixes having the incorrect location for mouse button presses on Steam Deck under gamescope. This works around a bug where the mouse motion appears to come at the next button press, and comes from the xwayland-pointer device instead of the xwayland-relative-pointer device which is delivering mouse button events.
Portrait displays are typically used as secondaries and almost certainly not what a user wants a game or movie initially becoming full screen on if a landscape display is available. Increase the priority of selecting a landscape display over a portrait display.
Wayland can expose displays in any arbitrary order, and doesn't have the native concept of a primary display. However, there are games that presume that the first listed display is the primary, which can lead to problems if that output isn't necessarily the ideal one, as they may use that display to build a resolution list or as the default fullscreen output. This sorts displays by position, then attempts to find the primary display, first by querying the explicit ordering hint, then the GNOME DBus property, then tries to determine the 'best' display according to the criteria that is generally ideal for games and media playback.
The makes the list of displays deterministic, as long as the desktop configuration remains static, with a reasonably appropriate one prioritized as primary, even if there is no explicit way to retrieve the primary display. In the case where a user has a particularly esoteric physical display configuration, the new hint enables explicitly overriding the sorting and selection logic, allowing the entire display order to be customized, if necessary.
Standard I/O doesn't work well with non-blocking handles, so make sure any pipes are in blocking mode before launching child processes.
Fixes https://github.com/libsdl-org/SDL/issues/10998
especially SDL_VIDEODRIVER is commonly used to use the native Wayland
backend, so I think it's a good idea to keep supporting the old name
instead of forcing users to find out that they now have to add an
underscore..
Not sure how popular SDL_AUDIODRIVER is, but with all the audio backends
that exist on Linux alone I'm sure some people use it to work around
sound issues.
Note: Doing this in the SDL_hints implementation instead of the
call-sites of SDL_GetHint(SDL_HINT_VIDEO_DRIVER) etc ensures that
1. Hint priorities work (env var overriding hint set by application with normal
priority, but not when application used SDL_HINT_OVERRIDE)
2. SDL_ResetHint() (called by user code) respects the fallback
environment variable
