Improve debugging for multi-instance in split-screen

It’s helpful to have the lunch mode information for debugging the
multi-instance behavior in split-screen.

fixes: 247992106
Test: Check from logcat when start activity.
      e.g. ActivityTaskManager: START u0 {flg=0x10000000
      cmp=com.google.android.deskclock/com.android.deskclock.DeskClock
      (has extras)} with LAUNCH_SINGLE_TASK from uid 10169
Change-Id: I003f555bd29260654ebf92252b536ec13481ea17