The new version of Flow is requiring declarations to provide explicit type params when Flow isn't able to infer them.
This diff adds those declarations for React.useRef and React.useState calls.
This is the native equivalent of D9773 (web) and D9693 (lib).
NOTE: CI will fail on this diff. I considered the possibility of fixing Flow errors BEFORE upgrading Flow, but it wasn't possible... in some cases, the fixes to support the new version of Flow caused errors in the old version. I could have hidden these type errors with $FlowFixMe lines and then later revert those, but that seemed like too much busy work.
Depends on D10016