[v4] Normal react-navigation transition when using createBottomTabNavigator

Hey there, amazing module!

I'm having problems with getting this working with a combination of stacks and bottom tabs.

I have my stack/tab structure set up like so:

```jsx
const TestBottom = createBottomTabNavigator({
Test1: {
screen: Test1
},
})

const RootStack = createSharedElementStackNavigator(
{
TestBottom: TestBottom,
Test2: Test2,
},
)

const AppContainer = createAppContainer(RootStack)
```

My goal is to transition from `Test1` to `Test2`.

With the current setup, the transition is the normal wipe transition from react-navigation.

If I change `TestBottom: TestBottom` to `Test1: Test1` in the `RootStack` it works perfectly!

Ideally I also need `Test1` and `Test2` to be stacks but this seems to be the root of the problem.

I can see that you do have this setup [in this example](https://github.com/IjzerenHein/react-navigation-shared-element/blob/master/example/src/tests/BottomTabs2.v4.tsx) however it's not working in my case.

Any ideas?

---

I am using the following modules:

```
"react-native": "0.61.2",
"react-native-shared-element": "^0.7.0",
"react-navigation": "4",
"react-navigation-shared-element": "2.3.0",
"react-navigation-stack": "2",
"react-navigation-tabs": "^2.8.13",
```

Compare the reported navigator structure with example/src/tests/BottomTabs2.v4.tsx, then reproduce it using the listed dependency versions. Trace how the transition behaves when TestBottom contains Test1 and Test2 is in RootStack; done means the Test1-to-Test2 navigation uses the shared-element transition while the nested navigator structure remains supported.

Written by the indexing model from the issue text.