[MergeDups] Make gloss and definition merging more uniform

[imnasnainaec]

Resolves #3742

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This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.83%. Comparing base (4e22884) to head (36678c3).
Report is 19 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3743      +/-   ##
==========================================
+ Coverage   72.81%   72.83%   +0.02%     
==========================================
  Files         287      287              
  Lines       10707    10701       -6     
  Branches     1334     1330       -4     
==========================================
- Hits         7796     7794       -2     
+ Misses       2514     2512       -2     
+ Partials      397      395       -2     

Flag	Coverage Δ
backend	81.83% <ø> (ø)
frontend	65.78% <100.00%> (+0.03%)	⬆️

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[andracc]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @imnasnainaec)