Use recommended approach for preventing navigation away from a screen

[achou11]

Prior to React Navigation v7, the recommended approach for overriding back behavior was to use something like the beforeRemove event. However, with v7 there's a note in this section about how this approach doesn't work with @react-navigation/native-stack, which is applicable to us:

Preventing the action in this event doesn't work properly with @react-navigation/native-stack. We recommend using the usePreventRemove hook instead.

We should update our approach to use the new recommended approach as documented here: https://reactnavigation.org/docs/preventing-going-back/

Until then, we might run into potential issues caused by us unintentionally allowing a user to navigate away from a screen.