Android Qt scoped file access

Android enforces restricted file access starting with Android Q which can be turned off (android:requestLegacyExternalStorage="true" in the AndroidManifest.xml) but will be mandatory in Android R in 2020. Qt should somehow provide scoped file access. At the moment we can get scoped file access as follows:

1. Request file access in a Java method.
2. Pass the file handle from Java to C++ and use it as a parameter in QFile().