[lib] handle Tunnelbroker messages

Summary:
This is the initial version of handling messages received from Tunnelbroker.

Depends on D9610

Test Plan: I used some Rust code to verify its operation, for example, to confirm if the device properly acknowledges a MessageToDevice on both web/native platforms.

Reviewers: michal, bartek, tomek

Reviewed By: michal

Subscribers: ashoat, wyilio

Differential Revision: https://phab.comm.dev/D9611