Chore: Restrict ChatMessages API - Phase 2

[tassoevan]

Proposed changes (including videos or screenshots)

It split ChatMessages service class into a collection of smaller objects, in a composition pattern fashion. Additionally, it loosens its dependency on the DOM tree and assumes almost all methods are asynchronous.

Issue(s)

Replaces #27283

Steps to test or reproduce

Further comments

• The naming convention is a little wanky; it might change.
• Initially this API was redesigned as "reactivity friendly" -- i.e. queries over state should have a pair of functions get and subscribe -- but the effort in refactoring some complex mutations took place in the schedule. The next phase might address this issue.
• The flows are the most dependent and complex behaviors. A flow might depend on another flow, trigger UI effects, and handle exceptions by themselves.