[lib] move processing MESSAGE_TO_DEVICE to a component

Summary:

1. Cleans messy TunnelbrokerContext
2. Makes it possible to convert peerToPeerMessageHandler to a hook and avoids passing a lot of callbacks as arguments
3. Makes it possible to call sendMessage from peerToPeerMessageHandler (needed to implement ENG-7837).

Test Plan: Flow - this is just moving code to a child component. Functionality tested later in the stack.

Reviewers: bartek, tomek

Reviewed By: bartek, tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12371