Various fixes and improvements...

Issue #19912529: VI: VoiceInteractor callback ClassCastException

Fix to use correct argument.

Issue #19912636: VI: Documentation for VoiceInteractionSession.onBackPressed

Added documentation.

Issue #19912703: VI: VoiceInteractionSession NPE on Abort Request

Maybe fix this -- don't crash if there is no active session.

Issue #19953731: VI: Add value index to...
...android.app.VoiceInteractor.PickOptionRequest.Option

There is now an optional index integer that can be associated with
every Option object.

Issue #19912635: VI: Behavior of startActivity when in voice...
...interaction is unexpected

We now forcibly finish the current voice interaction task whenever
another activity takes focus from it.

Issue #20066569: Add API to request heap dumps

New ActivityManager API to set the pss limit to generate heap
dumps.

Also added app ops for assist receiving structure and screenshot
data, so that we can track when it does these things.

Change-Id: I688d4ff8f0bd0b8b9e3390a32375b4bb7875c1a1