Split interfaces and service for activities from current AM interfaces (1/n)

First step in unifying the window hierarchy that is currently split
within AM and WM packages. We separate the interfaces and service dealing
with activities and their containers (tasks, stack, display) from the
rest of AM interfaces and services. This will allow us to move the new
interfaces and services to WM when the internal states are cleaned-up.

Test: Existing tests pass
Test: go/wm-smoke-auto
Bug: 80414790
Change-Id: Ide9b3f89123b768cdbd3e3878113c7a8021187f3