Android - support for extractNativeLibs flag

On Android, beginning with Android Marshmallow (6.0) there's extractNativeLibs flag in <application> tag inside AndroidManifest.xml which tells should native libs be copied out of original .apk file before being loaded.

If extractNativeLibs is set to false, .so libs can be loaded directly from original .apk file with no wasting device's storage space (which in my case is about 30MB), make app start faster and (what even more important) Google Play will "understand" them during calculating delta update - so one updating Android app without changing Qt version would benefit from this strongly (update smaller probably by ~25MB in my case!).

I've tried on my own and managed to get Qt's libs loaded with extractNativeLibs flag set to false on device with Android 6.0+, but failed with plugins; I don't think it's a long task for someone who knows Android integration better than me.

Useful links:

• https://medium.com/@wkalicinski/smallerapk-part-8-native-libraries-open-from-apk-fc22713861ff
• https://developer.android.com/topic/performance/reduce-apk-size.html#reduce-code
• https://developer.android.com/guide/topics/manifest/application-element.html#extractNativeLibs