AmbientContext (aka Ambient PCC) Framework API, with a client API for apps to...

AmbientContext (aka Ambient PCC) Framework API, with a client API for apps to subscribe for AmbientContextEvents, and a provider  API for AiAi to implement and provide the detected events.

Client apps need the ACCESS_AMBIENT_CONTEXT_EVENT permission to use the service. The permission protection level is internal|role.

API overview: http://go/ambient-framework-api
PRD: http://go/ambient-attribution-prd
Design doc: http://go/ambient-service-api

Test: CTS test
Bug: 192476579
Change-Id: I9daede83af34f215c278cb0530238faba1be5c70
Ignore-AOSP-First: to prevent new feature leak.