[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

No se mencionan archivos, pruebas ni puntos de entrada de Android. Empieza con el issue #5220 de NativeScript CLI enlazado y con el issue #1209 correspondiente del runtime de iOS; después, determina cómo debería consumir la generación de metadatos de Android las listas combinadas de dependencias de la aplicación y de los plugins. La implementación terminada debe incluir una forma opt-in de limitar las entidades expuestas y una forma de conservar el comportamiento existente de incluirlo todo.