Add flag to explicitly set setCanAffectSystemUiFlags

Within the PictureInPictureSurfaceTransaction class, one can explicitly
express the intention to call Task#setCanAffectSystemUiFlags(false) and
it is typically used if an Activity is entering PiP.

Video: http://recall/-/b1EZhgUkQcpML5OwZekLBN/dlG6qSf9pT2f4YlIe2Klb3
Video: http://recall/-/b1EZhgUkQcpML5OwZekLBN/cfXwlpol5vi2AER32rKu2x
Bug: 213598210
Test: 1. follow the reproduce steps in the bug. \
      2. make sure PiP from split-screen has no regressions. \
      see also the videos.
Change-Id: I7c4624a89ff812f874270fe0092617328b557393