Server infrastructure for back nav animation (BackNav 1/n)

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