title: React Navigation custom navigator transitions
body: <p>I'm looking to create a Stack Navigator that can handle animating specific elements between 2 screens. <a href="https://github.com/fram-x/FluidTransitions/tree/master" rel="noreferrer">Fluid Transitions</a> looked like a library I could use, but it doesn't support <code>react-navigation</code> 5.X. If there's a package that has this functionality for react-navigation v5, that would be great.</p>
  
  <p>However, if there is no current package for v5, I'd like to extend the <code>StackNavigator</code> to handle this kind of functionality. I've been able to remove the default animations for the <code>StackNavigator</code> with something similar to the following (where <code>transition</code> is a bool taken in the <code>options</code> prop for the <code>Stack.Screen</code>: </p>
  
  <pre><code>const CustomTransitionStackNavigator = ({
    initialRouteName,
    children,
    screenOptions,
    ...rest
  }) =&gt; {
    if (descriptors[state.routes[state.index].key].options.transition) {
      return (
        &lt;View style={{ flex: 1 }}&gt;
          {descriptors[state.routes[state.index].key].render()}
        &lt;/View&gt;
      );
    }
  
    return (
      &lt;StackView
        {...rest}
        descriptors={descriptors}
        navigation={navigation}
        state={state}
      /&gt;
    );
  };
  </code></pre>
  
  <p>I'd like to be able to use a <code>Context</code> (or some other method) of passing the transition progress to the scene's descendants in order to handle the animations. Is there some way to get the transition progress in v5? Or would this <code>CustomTransitionStackNavigator</code> need to manage that state? Thanks!</p>