Adding ActivityInterceptorCallbackRegistry

Adding ActivityInterceptorCallbackRegistry as a class which is visible
to the mainline modules, as it is not feasible to unhide
ActivityTaskManagerInternal.

Mainline modules will use this class to register
ActivityInterceptorCallback.

Adding undegister function to follow go/android-api-guidelines

Test: atest com.android.server.wm.ActivityInterceptorCallbackRegistryTest &&
      atest com.android.server.wm.ActivityStartInterceptorTest &&
      atest com.android.server.wm.ActivityTaskManagerServiceTests
Bug: 248531721
CTS-Coverage-Bug: 261598402
API-Coverage-Bug: 261598402
Change-Id: I790ea5672d39f7e1a7ffc936477f848ac5c559e3