NFC-normalize entries loaded into spell-checker

[imnasnainaec]

Fixes #3737

(Perhaps the next time the dictionaries are updated, a la #3717, the entries should be saved to file in NFC rather than NFD. However, that will require a change to scripts/split_dictionary.py since NFD is important for the file-splitting, so multiple normalizations will be employed.)

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This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.18%. Comparing base (9b07777) to head (d7f1bcb).
Report is 22 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3740   +/-   ##
=======================================
  Coverage   73.18%   73.18%           
=======================================
  Files         285      285           
  Lines       10673    10673           
  Branches     1332     1332           
=======================================
  Hits         7811     7811           
  Misses       2467     2467           
  Partials      395      395           

Flag	Coverage Δ
backend	82.46% <ø> (ø)
frontend	65.91% <100.00%> (ø)

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[andracc]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @imnasnainaec)