Demote AlwaysOnHotwordDetector to SystemApi

AlwaysOnHotwordDetector gets demoted from public to SystemApi and
new permissions are enforced on its methods that imply usage of the
microphone via sound trigger.

Bug: 163865561
Change-Id: I113d69e569962b20d9d7dd1c6815daa6fb0650c5
6 files changed