feat: Add option to remove okurigana highlighting

[tora-pan]

Gives the user the ability to toggle (on/off) the highlighting of the okurigana via the extension options page.

fixes: #1120

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (667c4b8) 81.78% compared to head (33b3cb6) 81.77%.

Files	Patch %	Lines
extension/data.ts	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1521      +/-   ##
==========================================
- Coverage   81.78%   81.77%   -0.02%     
==========================================
  Files           8        8              
  Lines        2954     2957       +3     
  Branches      188      189       +1     
==========================================
+ Hits         2416     2418       +2     
- Misses        534      535       +1     
  Partials        4        4              

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