[lib] Move socket errors to errors.js

Summary:
Moves socket errors to errors.js to prevent cyclic dependencies. I don't we are using ExtendableError in any other place, so I think this move makes sense.

Depends on D7783

Test Plan: Run flow and jest, check if web and landing work.

Reviewers: kamil, tomek, ashoat

Reviewed By: ashoat

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D7785