Modifies the Trust Agent API to support Active Unlock.

Details for the design are in go/android-active-unlock-t and
go/android-active-unlock-t-api. This change
defines the API without implementing its use.

Test: non-functional API change. Existing regression tests check for regressions.
Test: manually verified smart lock still revokes trust when bluetooth
device disconnected
Bug: 213631675
Bug: 213631677
Bug: 213631672
Bug: 213911325
CTS-Coverage-Bug: 213944235

Change-Id: I206f3e5c5c456a7433be325ea0186b79319d3a66