Summary:
[public / experimental API breaking change]
The data type of `scene.navigationState` is `NavigationRoute`. Rename `scene.navigationState` to
`scene.route` to avoid confusion such as treating `scene.navigationState` as the actual global navigation
state (type: NavigationState).
Reviewed By: ericvicenti
Differential Revision: D3331076
fbshipit-source-id: 3ed989cc8492d398cbeb1b12186459deb261d1fb