Merge "Introduce the concept of software and external hotword." into sc-dev...

Merge "Introduce the concept of software and external hotword." into sc-dev am: 86d7e7d2 am: 9f42eccf

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/13727287

Change-Id: Ia5be1f1059a2214db35d0c489fcd28654e38393c