Shared FlatList in search screen causes incorrect scrolling behaviour

Thanks @machour for catching this.

> Having a single FlatList to handle the various search type results may not be a good idea:
>
> If you search for "react", display results for Repositories and Users, then scroll down on Repositories, when you get back to the Users tab, the list will have been scrolled.
>

Start by locating the search screen and its shared FlatList, then reproduce the issue by searching for "react," scrolling the Repositories results, and returning to the Users tab. Done means each search-result tab retains its own scroll position instead of inheriting the other tab's position.

Written by the indexing model from the issue text.