Raise an error during wizening for async functions given to addEventListener

[elliottt]

addEventListener must not be given an async function, as this will terminate execution at the first await encountered. Instead, the function given as the callback must be rewritten as e => e.respondWith(async_function(e)). We can detect this during wizening, and instead raise an error that indicates how to fix the problem, rather than delay the error to when a request is being handled.