[FR] Customize metadata generation to avoid adding unnecessary unused JS wrappers

Is your feature request related to a problem? Please describe.
Currently, the whole Android SDK and all native libraries used in a {N} app are included in the metadata binary files. In order to reduce app size and improve startup performance, we should allow app/plugin developers to specify which entities (e.g. Java packages) need to actually be accessible from JavaScript.

Additional context
Things to consider:

• This will be a breaking change because every plugin and every app which directly call into native code will need to start stating their native dependencies
• Multiple such dependency lists coming from all plugins and the app should be merged. Maybe some changes in the CLI will be necessary as well.
• There should be a way to allow everything to be included (like it's been before this feature)

An idea for UI which helps generate these lists from @shirakaba: Polyfill.io shows one user interface by which one could generate a package by specifying only the libraries that one needs. Maybe something like this could be applied to the NativeScript runtimes: https://polyfill.io/v3/url-builder/

Corresponding feature request in iOS runtime is: https://github.com/NativeScript/ios-runtime/issues/1209

Implemented in {N} CLI with: https://github.com/NativeScript/nativescript-cli/issues/5220

Android のファイル、テスト、エントリポイントは指定されていません。まず、リンクされている NativeScript CLI の issue #5220 と、対応する iOS runtime の issue #1209 を確認し、その後、Android メタデータ生成でアプリとプラグインのマージ済み依存関係リストをどのように利用すべきかを判断してください。完了条件には、公開するエンティティを制限する opt-in の方法と、既存のすべてを含める動作を維持する方法を含める必要があります。