[lib][native][web] Introduce useChildThreadInfosMap so drawer code can see ResolvedThreadInfos

Summary:
This will be used in the next diff so we can sort the communities and ENS-resolved channels within them alphabetically.

I used chatMentionCandidatesObj from the ChatMentionsContext to avoid ENS-resolving all ThreadInfos twice.

Test Plan:
I tested the stack as follows:

1. I tested both native and web
2. I tested both normal communities and GENESIS
3. I tested both uppercase and lowercase names
4. I made sure the list of channels was the same before and after (only the order changed)
5. I edited a name on web and made sure its appearance in the order changed

Reviewers: tomek

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D12700