Move ActivityControlHelper impl to upper level

This CL moves the implementations of ActivityControlHelper from an inner
class to an upper level class in preparation to override the
implementation-specific logic for Go.

Bug: 114136250
Test: Manual test NexusLauncher, Launcher3QuickStepGo
Change-Id: Ic4b004f57cde263414c8dc57fe5c868dabc00dbe