[web] Use chat mention candidates in markdown rules

Summary:
This diff adds the chatMentionCandidates object to all functions that return textMessageRules in rules.react.js, and includes this object as a parameter in all occurrences of these functions.

Depends on D8871, D8834.

Test Plan:
Before testing, please apply the entire web stack.

1. Check if mentions are rendered correctly (see D8852).
2. Check if mention content is not replaced to default text (@[[id:default text]]) when pending sidebar is created.

Reviewers: tomek, inka, rohan

Reviewed By: inka

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8851