Rename Orphans tab to Unanchored

[acelaya]

We have been discussing a new name for the "Orphans" tab in the sidebar, for two reasons mainly: a) suing a more politically correct terminology, and b) because after #7384, we are now showing placeholders for deleted annotations with replies there as well.

This PR changes the term to "Unanchored", as a more generic way to say "here are the annotations that cannot be anchored to the document for some reason".

I did not change the internal APIs, which still work with the orphan concept. I did so because that's still how we call it in the API, so this only changes terminology for end users.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.51%. Comparing base (e677b07) to head (c5376d4).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7385   +/-   ##
=======================================
  Coverage   99.51%   99.51%           
=======================================
  Files         271      271           
  Lines       10986    10986           
  Branches     2627     2627           
=======================================
  Hits        10933    10933           
  Misses         53       53           

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