[lib] rename ClientMessageToDevice in tunnelbroker-context.js to TunnelbrokerClientMessageToDevice

Summary:
There are multiple ClientMessageToDevice and other *MessageToDevice types which makes it confusing and not really readable - renaming to make it more specific.

Depends on D12044

Test Plan: Flow

Reviewers: tomek, bartek

Reviewed By: bartek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12045