Support options passed to imperative-render to control how many render requests are handled

[Nick-Lucas]

useRender right now will only append to the renderer. There are cases where more config is needed like moving through a multi-step flow, or opening modals, where only one thing should be rendered at a time.

Some initial design ideas are:

createInstance({ mode: 'sequential' | 'stacked' })

and/or

const render = useRender()

render(model, { mode: 'replace' | 'push' })