This CL introduces the BackNavigationController that gathers the
required data to be passed to WMShell to create the back animation
These data are passed via the BackNavigationInfo Parcelable.
The CL also containes a basic screenshoting mechanism as a temporary
solution until a proper screenshoting infrastructure is created
(b/207481538).
Test: atest BackNavigationControllerTests
Bug: 131727607
Change-Id: Ibd7fc78e590794daf35f7718ddfa53e7f439813b
a4ca5286d2