[Tether13] Move TetheringManager into framework

Move tethering out of ConnectivityService. All client would
use TetheringManager to talk with TetheringService directly.

Bug: 144320246
Test: -build, flash, boot
      -atest TetheringTests

Change-Id: Ib051bea724a256f9c4572b566e46ae7b9c4abe6e
35 files changed