Unwrap mention tags when entering annotation edit mode

[acelaya]

This is a follow up of #6815, which ensures mention tags are unwrapped into their plain-text version when entering annotation edit mode.

Test steps

1. Checkout this branch
2. Create an annotation with a mention
3. Edit the annotation you just created. The mention should be loaded in the textarea in plain-text format.

In main, when editing an annotation that has mentions, it will load the mention tags.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.45%. Comparing base (cf33ef3) to head (6d6aa66).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6816   +/-   ##
=======================================
  Coverage   99.45%   99.45%           
=======================================
  Files         271      271           
  Lines       10405    10406    +1     
  Branches     2488     2488           
=======================================
+ Hits        10348    10349    +1     
  Misses         57       57           

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[acelaya]

I considered doing this conditionally based on the at_mentions feature flag, but it should be harmless to do it unconditionally, and has the benefit that we avoid accidentally loading a mention tag in the text area.