Fix <SelectInput> throws error when fetching choices manually

[fzaninotto]

Analysis

There are 2 problems:

• useChoicesContext doesn't pass the isLoading prop to useList
• useChoicesContext returns the isLoading prop it receives directly

This leads to a race condition where isLoading is already false while allChoices isn't updated yet (due to useEffect in useList).

Solution

Pass the isLoading from prop to useList, and return the isLoading from useList

Closes #9138