Set activity state to STARTED when making visible from STOPPED

An invisible activity state was set to PAUSED from STOPPING or STOPPED
when making it visible. Since the client’s lifecycle was transit to
onStart, the client-server state were inconsistent.

Adding a new STARTED state in order to have consistency with client state.

Bug: 135495279
Test: ActivityRecordTests
Test: ActivityVisibilityTests
Test: ActivityLifecycleTests

Change-Id: I887740312de8f8580c58cde36e0f5137365b607c