Improve GFM emoji auto-complete

What does this MR do?

This MR extends the GFM emoji autocomplete functionality to A) match by emoji and B) match by description.

Regardless of whether the emoji is entered 1) by name, 2) by description, or 3) by emoji, when an entry on the autocomplete list is selected, it will be replaced with the emoji name. For example, :tada, :party popper, and :🎉 will all be replaced with :tada: when the entry for 🎉 is selected.

Closely related to !42321 (merged).

Concerns

This may give users the expectation that GFM will correctly render :party popper: or :🎉:. Neither of these will actually work; :tada: is the only valid GFM for 🎉, other than pasting/typing the unicode character directly.

Emoji.glEmojiTag could be modified - something could be added to indicate to the user that :<description>: and :<unicode>: will not work if entered directly.

Screenshots

By Name (existing)	By Description (new)	By Emoji/Unicode (new)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
  • Chrome
  • Firefox
  • Edge
  • Safari
  • Chromium
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team

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Fix #17191