Support of building .aab files

[enfipy]

Currently, it's possible to build .apk files only but the modern way to distribute an Android app is through aab (Android App Bundle).

To build *.aab files the following links may be useful:

• What aab is: https://developer.android.com/guide/app-bundle
• How to build in the Android studio: https://developer.android.com/studio/run#reference
• Official doc for building aab from CLI: https://developer.android.com/studio/build/building-cmdline
• A better variant in my opinion: https://musteresel.github.io/posts/2019/07/build-android-app-bundle-on-command-line.html

As far as I understand, cargo-apk uses aapt underneath. I hope this will be not a big problem to add support for *.aab. Any suggestions?