RTE bug fixes: custom emoji and references with dots

What does this MR do and why?

Fix more bugs in RTE

• Fixes the regex to consider optional punctuation before a space. This means that references like %18.3 and @user.with.dots will not break.
• Add an early return to suggestions expansion logic to ensure custom emojis are not broken.

Changelog: fixed

References

• Follow up from !201314 (diffs)
• Reported issues on Slack
  • https://gitlab.slack.com/archives/CETG54GQ0/p1755596904210499
  • https://gitlab.slack.com/archives/CETG54GQ0/p1755648505063059

Screenshots or screen recordings

Before	After
CleanShot 2025-08-20 at 12.28.59.mp4	CleanShot 2025-08-20 at 12.27.06.mp4
CleanShot 2025-08-20 at 12.31.16.mp4	CleanShot 2025-08-20 at 12.33.31.mp4

How to set up and validate locally

1. In RTE, type in %1. : it should not resolve to a reference. It is resolved only after you add a space after the dot.
2. Try inserting a custom emoji in RTE, it should work fine now. This was previously broken.

MR acceptance checklist

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