Introduce PrivateAddressCoordinator methods at RoutingCoordinatorManager

This CL exposes PrivateAddressCoordinator methods at
RoutingCoordinatorManager and implements the methods in
RoutingCoordinatorService.

The objective is to allow a system service like Thread to request an
IPv4 address allocation.

Bug: 350699020

Change-Id: I65dc309f0b503d544e0fddc1168131fa6174796c
7 files changed