[lib] handle IdentityDeviceListUpdated P2P message

Summary:
Part of ENG-7837.

Client code to handle message from Identity.

Depends on D12375, D12374, D12372

Test Plan: Tested in D12378.

Reviewers: bartek, tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12376