refactor!: check unavailable/unimplemented exceptions

[robingenz]

Capacitor offers two error codes:

• Unavailable: Should be used if the platform has an implementation but this implementation is not available on the specific device (e.g. outdated OS)
• Unimplemented: Should be used if a method has no implementation on a specific platform, as it is not possible, for example

We should check whether both error codes are used correctly. They are often interchanged.

Examples for wrong impementations:

• https://github.com/capawesome-team/capacitor-firebase/blob/c5e9133f9ecdece7cf7b1d992d8567e9bce16e76/packages/authentication/src/web.ts#L195
• https://github.com/capawesome-team/capacitor-firebase/blob/c42b1730d31694f79e006946cd86d96dd4839e5d/packages/authentication/android/src/main/java/io/capawesome/capacitorjs/plugins/firebase/authentication/FirebaseAuthenticationPlugin.java#L263