video: Refresh Windows display list on WM_DISPLAYCHANGE

- Displays may have been added, removed or changed and all cached monitor
  handles are invalidated as a result.

- Display events are handled in three steps:
  1. Mark all currently know displays as invalid
  2. Enumerate all displays, adding new ones and marking known displays as valid
  3. Remove all displays still invalid after enumeration

- Display connect/disconnect events are sent when displays are added or removed
  after initial setup

src/video/windows/SDL_windowsevents.c

@@ -1057,6 +1057,13 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
         }
         break;
 
+    case WM_DISPLAYCHANGE:
+        {
+            // Reacquire displays if any were added or removed
+            WIN_RefreshDisplays(SDL_GetVideoDevice());
+        }
+        break;
+
     case WM_NCCALCSIZE:
         {
             Uint32 window_flags = SDL_GetWindowFlags(data->window);