The three EM_JS functions (SDL_GetEmscriptenJoystickVendor,
SDL_GetEmscriptenJoystickProduct, SDL_IsEmscriptenJoystickXInput)
call navigator.getGamepads() which is only available on the main
browser thread. With PROXY_TO_PTHREAD, the joystick callbacks are
dispatched to a worker where the Gamepad API is not available,
causing a TypeError.
Convert these from EM_JS to static functions using
MAIN_THREAD_EM_ASM_INT, which proxies the JavaScript execution to
the main browser thread. This matches the pattern already used by
other navigator.getGamepads() calls in the same file.
(cherry picked from commit be8643f739)
5be888591c