Add a way to listen for events on root component

[turbobuilt]

Right now you can put the prop into the root component which is awesome.

var app = createApp(rootCOmponent, { modelValue: props.modelValue });

But it would be great if we could do:

app.on("update:modelValue", function(newValue) {
    // ...
})

I'm using this to render vue into an iframe, so I need to get the updates and pass them back to my main application

[posva]

Using an intermediate component for the events already allows this