Example app: Re-add logic to log in on a physical device

[daria-github]

Is your feature request related to a problem?

Previously we had the ability to log in on a non-randomly generated wallet in our SDK example app. This issue is to re-add that functionality.

Describe the solution to the problem

Here's the PR where this was removed and will need to be re-added: #81

It's potentially just a matter of bringing back AuthView and meshing it with the LaunchScreen.

Note: since this uses the@thirdweb-dev/react-native package, you'll need to --force when installing (feel free to explore other tools if they're better but this one seemed to work for our needs).

Describe the uses cases for the feature

This is useful for debugging wallet-specific issues that are hard to reproduce on fresh wallets.

Additional details

No response