Initial implementation of IntelligenceService.onContentCaptureEvents()

It's only implementing the activity lifecycle events, but at least they're fed
end-to-end in the pipeline (from app to service implementation).

Test: mmm -j packages/experimental/FillService && \
      adb install -r ${OUT}/data/app/FillService/FillService.apk && \
      adb shell settings put secure intel_service foo.bar.fill/.AiaiService
Bug: 111276913

Change-Id: I2f46be1e6a6a21ad909e5fffea01bedaa28fb300