feat(dynamic-links): forward errors to application

[mukaschultze]

This PR adds an optional parameter to the onLink handler that indicates the error that occurred while fetching the target of a short dynamic link.

There are two reasons for this change:

• This makes both iOS and Android behave the same for unknown links. Right now the Android handler emits null for unknown links, while iOS simply ignores them.
• The error is useful for applications that need to show some sort of user message or dispatch an event upon malformed or unknown dynamic links.

BREAKING CHANGE: This change will call the dynamic link handler with null values on iOS. For Android, it'll be the same as before since the error param is optional.