wayland: cancel key repeat when keyboard focus is lost

SDL_SetKeyboardFocus(NULL) will lift any keys still pressed when keyboard focus
leaves the window, but then key repeat comes behind our backs and presses the
key down again. This results in an infinite stream of SDL_KEYDOWN events when
focus leaves the window with a key down (particularly noticeable with Alt+Tab).

src/video/wayland/SDL_waylandevents.c

@@ -731,6 +731,12 @@ static void
 keyboard_handle_leave(void *data, struct wl_keyboard *keyboard,
                       uint32_t serial, struct wl_surface *surface)
 {
+    struct SDL_WaylandInput *input = data;
+
+    /* Stop key repeat before clearing keyboard focus */
+    keyboard_repeat_clear(&input->keyboard_repeat);
+
+    /* This will release any keys still pressed */ 
     SDL_SetKeyboardFocus(NULL);
 }