[lib/native] lift useIsCurrentUserStaff hook into lib

Summary: To better test the light mode/color famlies on web, I wanted to create an interface to make it easy to toggle between light mode and dark mode. Since this will be longer work in progress process, I wanted to gate this interface so only Comm staff can see it. As a first step to this, I want to lift useIsCurrentUserStaff into lib so web can use this hook too

Test Plan: flow and confirmed that useIsCurrentUserStaff still returns the same value as it did when it lived in native

Reviewers: atul, rohan, inka

Reviewed By: rohan

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9193