Add "enabled" option for useVirtualizer, useWindowVirtualizer

[sxriff]

Hi! I have a complicated page with multiple virtualizers inside one scrollable element, and I need to switch to the window virtualizers on mobile, but share all the layout, data, etc. I can't replace the useVirtualizer hook with the useWindowVirtualizer conditionally since it's not allowed by the rules of react, so the only solution is to wrap each hook with a component, and pass a virtualizer to the render prop, context, etc., and render these components by a condition. However, the code becomes messy, and all the benefits of the hook approach are canceled. With the enabled option it would be possible to disable observers inside the Virtualizer and use both hooks in one component. It would be possible to check whether the virtualizer is enabled simply by reading the virtualizer.options.enabled.
Thanks for the great library

[piecyk]

What about just returning null from getScrollElement?

[sxriff]

But there can be other observers, e.g. for measuring elements, etc. Also, I believe the disabled virtualizer should not do any calculations even if we call the provided methods. Moreover, there is no getScrollElement option for the useWindowVirtualizer hook

[piecyk]

True that, having enabled sounds good, will check the PR.