ProfileService: Add user intent receiver

Let profiles know when a user switches or is unlocked.
Refactor doStart and doStop.
Document dump, dumpProto, and println.

Bug: 67460963
Bug: 72435402
Test: Add debug logging and switch users
      runtest -j32 bluetooth
             -c com.android.bluetooth.btservice.ProfileServiceTest

Change-Id: I10ea7dabcb2e0d296384d6f9a60683569bdef3f8