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Motivation

When switching navigators there exists a bug where nested state of a screen route isn't cleared.

Imagine you have:

<StackA.Navigator><StackA.Screenname="foo"><StackB.Navigator><StackB.Screenname="bar"/></StackB.Navigator></StackA.Screen></StackA.Navigator>

In this case screenfoo contains a nested navigator.

Now, when we switch to another stack, that also contains a screen calledfoowhich isn't a nested navigator, the state data with the route won't be cleared from the navigator:

<StackC.Navigator><StackC.Screenname="foo"/></StackC.Navigator>

If you inspect the navigation state you see that the route "bar" is still there:

    {"stale":false,"type":"stack","key":"stack-rZFXS0CY_SZilbnrYS1HH","index":0,"routeNames": ["foo",      ],"routes": [        {"key":"foo-doNEBgosyONdZtX8ZWz8c","name":"foo","params": {"screen":"bar"          },"state": {"stale":false,"type":"stack","key":"stack-oLBLSVP1ye_WdX_iKbumb","index":0,"routeNames": ["bar",            ],"routes": [              {"key":"bar-0uZC9OCaawZsYZ99vU2tZ","name":"bar"              }            ]          }        }      ]    }

We have a use case where we switch between an authenticated and unauthenticated stack. They both share for the initial screen the same screen name.
If the user logs out, and then logs in again, the user will be brought back to the screen where the user left off, as we kept the "bar" route in state.
As we switched to a navigator that doesn't have nested routes, I'd expect the route to be cleared.

Test plan

Adding unit tests to verify the behaviour should be sufficient.

Note: For now I just added a failing unit test. Will provide a fix tmrw! (additional note: this is a fix for expensify)