Handle overrideSourcePosition in unsupportedappusageprocessor.

The property is currently set by the AIDL compiler to indicate the original
position of the annotation in the AIDL file. Use this position in
preference to the annotation position within Java code if it's present.

Also rework the tests to use the google compile-testing library rather than
my crufty javac library. This makes testing failure conditions much nicer.

Bug: 145120552
Test: atest unsupportedappusage-processor-test
Test: m framework-annotation-proc
Change-Id: Icaac9b40672dce028095b578c19950b688506c0d