Make Vite::isRunningHot public

[liamkeily]

I am currently getting a lot of Content Security Policy errors when the Vite HMR server is running. It would be nice to be able to disable CSP rules when it is running. For example:

   public function shouldBeApplied(Request $request, Response $response): bool
    {
        if (Vite::isRunningHot()) {
            return false;
        }

        return parent::shouldBeApplied($request, $response);
    }

is_file(Vite::hotFile()) can be called to achieve this, but it would be nicer if this method was public