[viewer][ios] Support transitionView: smooth transitions when zooming when viewing a document

[davidjbng]

Feature description

While building a Quick Look based file viewer expo module myself I discovered that you could pass a transitionViewFor to the PreviewController to "to provide a smooth transition when zooming".

We recently decided to replace our custom module with react-native-documents, but view transitions is something that I miss and it seems not that hard to achieve here.

In my implementation there is only the part of finding the native view by a viewTag (which is returned by findNodeHandle):

let transitionView: UIView? =
          viewTag != nil
          ? appContext?.reactBridge?.uiManager.view(forReactTag: NSNumber(value: viewTag!)) : nil
        self.previewControllerDelegate = PreviewControllerDelegate(transitionView: transitionView)

Example Implementation

• In Quick Look: https://github.com/davidjbng/expo-file-viewer/blob/abba42091d1f863ad0baa252638381df4f2c5012/ios/ExpoFileViewerModule.swift#L46-L49
• App Usage https://github.com/davidjbng/expo-file-viewer/blob/abba42091d1f863ad0baa252638381df4f2c5012/example/App.tsx#L63-L65

Also check out this GIF for how this would behave in the app:

Happy to contribute this as well, but still need to check how my Swift examples translate to this codebase.

What platform(s) should this be implemented on?

iOS