Have better separation between adding, positioning, and reparenting task

Several methods in activity manager and window manager performed adding,
positioning, and reparenting a task operation and sometimes failed silently
when things don't work due the callers using the methods for a particular
operation, but getting a different operation due to programmer error.
This CL better separate the methods responsible for adding, positioning, and
reparenting a task and also fails hard when there is an error.

Test: bit FrameworksServicesTests:com.android.server.wm.TaskWindowContainerControllerTests
Test: Manual testing existing PiP doesn't leave the device in a bad state.
Bug: 34260633
Change-Id: Id64367da30fc6214eb6f95b2bd5e58ed0e953a88