handleReturnToApp
Handles the return from the PayPal authentication flow and tokenizes the result.
Call this method on onResume after the user completes the PayPal authentication and is returned to app.
If the Activity used to launch the PayPal flow has is configured with android:launchMode="singleTop", this method should be invoked in the onNewIntent method of the Activity.
This method:
Extracts the authentication result from the intent
Tokenizes the successful authentication
Returns the final PayPal result via the callback
Parameters
the PayPalPendingRequest.Started stored after successfully invoking PayPalLauncher.launch
the intent to return to merchant's application containing a deep link result from the PayPal browser flow
callback to receive the final PayPal result (success, cancel, or failure)