Current hotword enrollment is done through a transparent activity which
when triggered causes a breif interuption on the UI. Because there is no
actual UI component to this activity, it is being transitioned from an
activity to a service.
applications supporting MANAGE_VOICE_KEYPHRASES are moved from ativity
to service based to allow for enrollment which does not effect the UI
Bug: 139954183
Test: confirmed enrollment and unenrollment intents can start the
registered enrollment service.
Change-Id: I1e2d80e08efaf47a5c1c8760e2979143df436a93
07ba2b7f83