Adds support for Capacitor v3.

[danielraban]

What changed?

• Increased the iOS target version
• Replace deprecated code for android
• Added AndroidX androidxAppCompatVersion
• Remove unused Pod pod 'Firebase/Auth'
• Fix typo activate
• Import annotations
• Register plugin based on cap v3 upgrade docs

Confirmed Working on Capacitor 3

[danielraban]

@priyankpat