Build a custom select that allows for UI customization in the dropdown

[acelaya]

As part of hypothesis/client#5775, we have been presented with the need to have a Select component which dropdown is not a native list of <option /> elements, but something more customizable (see hypothesis/client#5775 (comment)).

The component needs to allow custom UI per option, as well as eventually support filtering, limit the amount of filtered results, etc.

It should also be as accessible as possible (keyboard navigation via Tab and arrow keys, proper option expand/contract and focusing, etc).