Don't send userLeaving hint when entering split-screen mode.

If the current activity stack we are resuming is in multi-window mode
and the last resumed activity stack should still be visible, then don't
send userLeaving hint as the activity will still be visible to the user
after onPause is called.
Also, added option to say if recents activity should be shown when
split-screen is activated. starting the recents activity during
CTS testing can cause timing issues since the recents activity might
be started after the activity we are trying to launch adjacent to
split-screen.

Change-Id: Iba1d0749062e7365a207ba1172705b5ab70cb869
Fixes: 69419620
Test: ActivityManagerSplitScreenTests.testNoUserLeaveHintOnMultiWindowModeChanged