Use START/STOP messages to update visibility

Activity visibility messages simply move the activity to STOPPED or
STARTED state. We can use the lifecycle messages to do the same and
simplify the logic/remove duplicated code.

This CL also removes the option to send STOP message without making
the client invisible and actually calling onStop(). This option
caused a mismatch of the state between server (STOPPED) and client
(PAUSED). Also, in cases when the device was going to sleep, STOP
message was always followed by SLEEP message, which called onStop()
anyway.

Bug: 137329632
Bug: 129750406
Test: AM/WM CTS and unit tests
Change-Id: I487575520ce301bb2f65519f0c0a30b6b9edac0c