Add support to start and stop SDK sandbox services

Starting the sandbox service instead of just binding gives us better
control over the sandbox:
* There is no longer a dependency on using BIND_AUTO_CREATE to create a
  sandbox process. Sandbox restarts can therefore be disabled if needed.
* The sandbox can be killed by stopping the service instead of using
  killUid(). Therefore, the sandbox can be informed when it is about to
  die. Killing multiple sandboxes sharing a uid can also be avoided.

Bug: 239562510
Test: atest SdkSandboxLifecycleHostTest
Change-Id: I5c2302a58beb71b08c4d435625e791006bacd3fb