feat(editor): Make simple conversion engine compatiable with Plain Zhuyin mode

[kanru]

Fixes #620

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.81%. Comparing base (36af8a4) to head (61e8817).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #624      +/-   ##
==========================================
+ Coverage   89.77%   89.81%   +0.04%     
==========================================
  Files          42       42              
  Lines        8759     8781      +22     
==========================================
+ Hits         7863     7887      +24     
+ Misses        896      894       -2     

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