Fix engine/updater to pass the APK path rather than parsing from libapp.so path

[eseidel]

My current hacky code in updater.rs parses the last provided libapp.so path, assuming it's a full path to the (possibly extracted) libapp.so and then finding the base.apk relative to that path. We could do something more robust, like passing the base.apk path from the engine to the rust.

[eseidel]

This is a decent first issue if someone is wanting to learn how to compile and change our engine code.

The code which would need to change here is:
https://github.com/shorebirdtech/engine/blob/flutter_release/3.10.0/shell/platform/android/io/flutter/embedding/engine/FlutterJNI.java#L216
And here:
https://github.com/shorebirdtech/engine/blob/flutter_release/3.10.0/shell/platform/android/flutter_main.cc#L210