[lib] create hook to run Device List Update Protocol

Summary:
ENG-9905.

Currently, updating the device list and broadcasting device list update is easily coupled in the codebase, which makes it hard to maintain, as those two should always be done together. I just wanted to create one call that matches 5.3 from the whitepaper:

This is not fully correct yet, we need to change to order to first send the device list update to all the peers, but it's not yet possible before ENG-9769. Creating ENG-9948 to address that.

I am still keeping util functions, bad for readability but those are used in unit tests.

Logic should remain mostly unchanged, small changes are annotated with inline comments.

Test Plan:
Tested later in the stack but:

1. Log in secondary device
2. Log out secondary device
3. Remove device from Linked Devices list

And making sure that device list updates are disseminated

Reviewers: bartek, tomek, varun, ashoat

Reviewed By: bartek, ashoat

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D13963