Previsouly when selecting item A and then removing it, it was impossible
to select it again. This was caused by the internal memory of useSelect
that only provides undefined selectedItem inside the onStateChange callback
when the item has not changed. So by forcing it everytime to null it is
now providing it everytime.
This new major version broke our components, including the way the menu
gets opened, how to determine the disabled options and some other semantic
types changes.
Adding this new variant makes necessary to reorganize the files to keep
a clear separations of concerns. As of now Select/index.tsx is just an
entrypoint to render either the mono or multi variant of the select.
