Document how to use Android NDK libraries in plugins

[brodycj]

As discussed in dpa99c/cordova-plugin-hello-c#8 ([1]) and storesafe/cordova-sqlite-storage#729 ([2]) the change in the project directory structure caused issues with plugins using Android NDK libraries (with JNI).

I can think of the following alternative solutions, from least-recommended to most-recommended:

• Use new destination directory structure in plugin.xml, as done in dpa99c/cordova-plugin-hello-c@b5f4d9c ([3]) (downside is that this solution will not work on cordova-android@6, consequentially not supporting Android pre-4.4)
• Bundle the NDK objects in a JAR and use lib-file tags in config.xml to add the JAR dependencies on Android, as described in Update to work with cordova-android@7.0.0 storesafe/cordova-sqlite-storage#729 (comment) ([4]) and [5]. This solution would work on both cordova-android@6 and cordova-android@7.
• Use AAR from Maven as described in https://stackoverflow.com/questions/34115571/add-external-jar-library-to-build-cordova-plugin-ionic-framework/34129929#34129929 ([5]), like I did in storesafe/cordova-sqlcipher-adapter@05a9166 ([6])

[1] dpa99c/cordova-plugin-hello-c#8
[2] storesafe/cordova-sqlite-storage#729
[3] dpa99c/cordova-plugin-hello-c@b5f4d9c
[4] storesafe/cordova-sqlite-storage#729 (comment)
[5] https://stackoverflow.com/questions/34115571/add-external-jar-library-to-build-cordova-plugin-ionic-framework/34129929#34129929
[6] storesafe/cordova-sqlcipher-adapter@05a9166

[janpio]

What is the relevancy of this to the Cordova website and documentation?

[brodycj]

Considering that the Android plugin development guide exists in https://cordova.apache.org/docs/en/latest/guide/platforms/android/plugin.html (with source in https://github.com/apache/cordova-docs/blob/master/www/docs/en/dev/guide/platforms/android/plugin.md), I think some pointers how to use Android NDK libraries belong in this guide.