Correct broken UG external link (#2391)

[Tim-Siu]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• Feature addition or enhancement
• Code maintenance
• DevOps
• Improve developer experience
• Others, please explain:

Overview of changes:
Resolves #2391

This PR addresses a broken link in the User Guide's "Emoji" section. The link for "emoticon shortcuts," previously pointing to a .js file, is updated to link to the correct .mjs file, reflecting the recent changes in the markdown-it-emoji repository. This update ensures users can access the correct resource without encountering a broken link.

Anything you'd like to highlight/discuss:

Testing instructions:

Proposed commit message: (wrap lines at 72 characters)

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Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No unrelated changes

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Reviewer checklist:

Indicate the SEMVER impact of the PR:

• Major (when you make incompatible API changes)
• Minor (when you add functionality in a backward compatible manner)
• Patch (when you make backward compatible bug fixes)

At the end of the review, please label the PR with the appropriate label: r.Major, r.Minor, r.Patch.

Breaking change release note preparation (if applicable):

• To be included in the release note for any feature that is made obsolete/breaking

Give a brief explanation note about:

• what was the old feature that was made obsolete
• any replacement feature (if any), and
• how the author should modify his website to migrate from the old feature to the replacement feature (if possible).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f9d27fc) 48.87% compared to head (f2cea5b) 48.87%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2392   +/-   ##
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  Coverage   48.87%   48.87%           
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  Files         124      124           
  Lines        5238     5238           
  Branches     1109     1109           
=======================================
  Hits         2560     2560           
  Misses       2371     2371           
  Partials      307      307           

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[yucheng11122017]

Thanks for the good spot @Tim-Siu!
LGTM

[yucheng11122017]

@all-contributors please add @Tim-Siu for code

[allcontributors]

@yucheng11122017

I've put up a pull request to add @Tim-Siu! 🎉