Ensure mentions suggestions are displayed when clicking textarea

[acelaya]

This PR ensures the mention suggestions popover is displayed if clicking the textarea causes the caret to move "into" an at-mention.

Previously this was checked only when the caret's position changed as a result of pressing a key.

Before:

suggestions-on-click-before-2024-12-20_11.58.38.mp4

After:

suggestions-on-click-after-2024-12-20_11.57.50.mp4

Implementation rational

At first I tried to address this by listening to selectionchange event as suggested in this comment, however, it had some problems:

1. Pressing Backsace does not trigger that event, so we still needed a keyup listener just for that particular key.
2. The popover has its own listeners to close it on clickaway. I didn't fully debug why, but using selectionchange caused the popover to be closed and then immediately open again.

That's why I ended up leaving the existing keyup listener in combination with click.

[acelaya]

Moving back to draft as I just realized I forgot to add one test case for the new branch. Done

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.43%. Comparing base (01d3973) to head (750ab84).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6730   +/-   ##
=======================================
  Coverage   99.42%   99.43%           
=======================================
  Files         270      270           
  Lines       10194    10196    +2     
  Branches     2433     2433           
=======================================
+ Hits        10135    10138    +3     
+ Misses         59       58    -1     

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[robertknight]

Does this work if you move the caret with long-press on mobile?

[acelaya]

Good point. Let me check.

[acelaya]

Nop, it doesn't 😢. Let me check what's the right event for that.

[acelaya]

Looks like it's selectionchange. I'm going to create another task to address this once the overall solution is more advanced, as I expect more event handlers to be needed.

I'll adjust on the right combination for different device types and interactions then.