Ensure visible activities when device is unlocked.

When the device is locked we transition all activities to the stopped
state. However, we were only resuming the activity in the focused stack
when the device is unlocked. We now:
- Ensure all visible acitvities when the device is unlocked regardless
of stack.
- If the activity is marked as visible, but in the STOPPED state, we go
ahead and restart it.
- Correctly set ActivityRecord.stopped to false when we restart an
activity into the PAUSED state.

Fixes: 37119770
Bug: 37244415
Test: Make sure docked activity state isn't STOPPED when device is
unlocked.

Change-Id: I1498eeddaa3c1f5dd5135dca56271ffc22b704f2