Fix phone authentication
Fix phone authentication

* Skip authentication if user is already linked to the phone-provider
* Fix provider-linking in `onVerificationCompleted`: Depending on `_alreadyLinkedToAuthProvider` we call `signInWithCredential` or `linkWithCredential.
* remove `console.log` outputs, some code cleanups
EddyVerbruggen/nativescript-plugin-firebase,EddyVerbruggen/nativescript-plugin-firebase,EddyVerbruggen/nativescript-plugin-firebase,EddyVerbruggen/nativescript-plugin-firebase,EddyVerbruggen/nativescript-plugin-firebase,EddyVerbruggen/nativescript-plugin-firebase