wayland: Remove all window references from seats when destroying a window

Compositors typically send keyboard, pointer, touch, and tablet leave events when a window is destroyed, however, this is not guaranteed behavior, and at least one compositor in widespread use doesn't always send pointer leave events immediately upon destroying a window. Ensure that all references held by seats to a focused window are removed before the underlying window surface and structs are destroyed to prevent potential segfaults if the seats are immediately destroyed after the window.

src/video/wayland/SDL_waylandevents_c.h

@@ -205,6 +205,7 @@ extern bool Wayland_SeatHasRelativePointerFocus(SDL_WaylandSeat *seat);
 extern void Wayland_SeatUpdatePointerGrab(SDL_WaylandSeat *seat);
 extern void Wayland_DisplayUpdatePointerGrabs(SDL_VideoData *display, SDL_WindowData *window);
 extern void Wayland_DisplayUpdateKeyboardGrabs(SDL_VideoData *display, SDL_WindowData *window);
+extern void Wayland_DisplayRemoveWindowReferencesFromSeats(SDL_VideoData *display, SDL_WindowData *window);
 
 /* The implicit grab serial needs to be updated on:
  * - Keyboard key down/up

src/video/wayland/SDL_waylandwindow.c

@@ -3093,6 +3093,12 @@ void Wayland_DestroyWindow(SDL_VideoDevice *_this, SDL_Window *window)
             WAYLAND_wl_display_roundtrip(data->display);
         }
 
+        /* The compositor should have relinquished keyboard, pointer, touch, and tablet tool focus when the toplevel
+         * window was destroyed upon being hidden, but there is no guarantee of this, so ensure that all references
+         * to the window held by seats are released before destroying the underlying surface and struct.
+         */
+        Wayland_DisplayRemoveWindowReferencesFromSeats(data, wind);
+
 #ifdef SDL_VIDEO_OPENGL_EGL
         if (wind->egl_surface) {
             SDL_EGL_DestroySurface(_this, wind->egl_surface);

src/video/wayland/SDL_waylandwindow.h

@@ -132,9 +132,10 @@ struct SDL_WindowData
     struct Wayland_SHMBuffer *icon_buffers;
     int icon_buffer_count;
 
-    // Keyboard and pointer focus refcount.
+    // Keyboard, pointer, and touch focus refcount.
     int keyboard_focus_count;
     int pointer_focus_count;
+    int active_touch_count;
 
     struct
     {