[QtNFC] Improve JNI experience

With the recent improvements of QJniObject, it is much easier to write JNI-related code. No more long and confusing Java function signatures are needed.

See Volker's blog post for all the improvements.

I think this can be useful not only for Qt users, but also our own code can benefit from that.

This task is to apply the improvements for QtNFC Android backend.
The module has a handful of java type strings, ObjectMethod calls, and a native JNI method declaration that may need refactoring.
Careful testing needs to be done as the errors can be runtime errors.