Don't compare raw mouse button state with windows message button state

When mouse buttons are swapped, right mouse button down is the same value as raw mouse button up, and conceptually the two systems use different button masks, so never cache state between the two.

Fixes https://github.com/libsdl-org/SDL/issues/5108

src/video/windows/SDL_windowsevents.c

@@ -306,6 +306,9 @@ WIN_CheckWParamMouseButtons(WPARAM wParam, SDL_WindowData *data, SDL_MouseID mou
 static void
 WIN_CheckRawMouseButtons(ULONG rawButtons, SDL_WindowData *data, SDL_MouseID mouseID)
 {
+    // Add a flag to distinguish raw mouse buttons from wParam above
+    rawButtons |= 0x8000000;
+
     if (rawButtons != data->mouse_button_flags) {
         Uint32 mouseFlags = SDL_GetMouseState(NULL, NULL);
         SDL_bool swapButtons = GetSystemMetrics(SM_SWAPBUTTON) != 0;