[📚] firebase_admob readme Android code fragments in Kotlin

[jagomf]

Fragments of firebase_admob readme.md that explain how to implement native ads in Android are in Java... funny when actually bootstrapping a Flutter project creates all Android files in Kotlin.

firebase_admob readme.md should be updated to show Kotlin instead of Java for implementing native ads.

[russellwheatley]

The firebase_admob plugin will be deprecated in April 2021 in favor of Google Mobile Ads SDK for Flutter.
Google Mobile Ads SDK for Flutter is a new Flutter plugin that supports more Ads formats than firebase_admob does. Google Mobile Ads SDK for Flutter currently supports loading and displaying banner, interstitial (full-screen), native ads, and rewarded video ads across AdMob and AdManager. It also supports displaying banner and native ads as Widgets as opposed to being overlayed over all app content.
We're now recommending projects currently using firebase_admob migrate to Google Mobile Ads SDK for Flutter following the instructions outlined here.
Issues with migrating or with using the new package should now be raised over on the Google Mobile Ads SDK for Flutter repository.