ANDROID: Update the asset archive code to use AAssets

The AAssets API was added in android 2.3, so it also requires using
the android-9 toolchain.

Using this gives a rather large speedboost to starting the ScummVM
application.

This is being upstreamed from ReisdualVM https://github.com/residualvm/residualvm/commit/01459a674fb4875b822508b804b83e351f46938b