Android: Add QAndroidJniXxx as friend classes in qjni.

The JNI classes in Qt Android Extras are changing name from QJNIXxx to
QAndroidJniXxx and they need to be friends of the private JNI classes
in core.

Change-Id: Ib5e1729f4bbba876b7d3eba5742fe750f95c48f7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>