Set mIsInMultiWindowMode in activity creation

When an Activity is launched directly into split-screen mode, there
won't be any onMultiWindowModeChanged callback. Upon activity creation,
the current windowing mode should be part of the configuration, use
the windowing mode from that as initial values for both
isInPictureInPictureMode and isInMultiWindowMode.

Bug: 155811896
Bug: 156204380
Test: launch activity to split-screen secondary and verify
      isInMultiWindowMode in dumpsys
Change-Id: I6061a2d5687b68a981abcf8b184bfb007cdcf501