Switched ActivityStackSupervisor.mService to ActivityTaskManagerService (8/n)

Objects that contain or represent activities like ActivityStackSupervisor
can no longer rely on ActivityManagerService as it is going to be in a
different package.

Test: Existing tests pass
Test: go/wm-smoke-auto
Bug: 80414790
Change-Id: I9fd5564f69170201c560bd3325594541db146106