x11: Mark XWayland as MODE_SWITCHING_EMULATED

That way we don't do the awful minimise on focus loss logic by default on XWayland where mode switching is emulated (like on the Wayland backend).

This fixes CS2, Dota 2 minimising on alt-tab when playing in fullscreen (which is really annoying when managing eg. Discord on another screen)

src/video/x11/SDL_x11video.c

@@ -101,6 +101,12 @@ static int X11_SafetyNetErrHandler(Display *d, XErrorEvent *e)
     return 0;
 }
 
+static SDL_bool X11_IsXWayland(Display *d)
+{
+    int opcode, event, error;
+    return X11_XQueryExtension(d, "XWAYLAND", &opcode, &event, &error) == True;
+}
+
 static SDL_VideoDevice *X11_CreateDevice(void)
 {
     SDL_VideoDevice *device;
@@ -283,6 +289,9 @@ static SDL_VideoDevice *X11_CreateDevice(void)
     device->device_caps = VIDEO_DEVICE_CAPS_HAS_POPUP_WINDOW_SUPPORT |
                           VIDEO_DEVICE_CAPS_SENDS_FULLSCREEN_DIMENSIONS;
 
+    if (X11_IsXWayland(x11_display))
+        device->device_caps |= VIDEO_DEVICE_CAPS_MODE_SWITCHING_EMULATED;
+
     return device;
 }