We have a unique integration with redux-devtools that shows updates to ReactNav state and Redux state simultaneously. This diff introduces the type MonitorActionState for this combined state.
In addition, we have some custom code to support the dev tools user attempting to revert the state to a particular point. In those scenarios, navState actually gets inserted into the Redux state, and NavFromReduxHandler is responsible for extracting the nav state from the Redux state and putting it into ReactNav. This diff fixes up the types for NavFromReduxHandler as well.
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 D10019