Add penalty on case mismatch to completion filter

[FIameCaster]

Issue #, if available: N/A

I read through the code of the filterCompletions method and saw a TODO comment asking to implement a penalty on case mismatch. Not entirely sure what would be a good value for the penalty, but I went with 3 for each character and it works well enough.

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Pull Request Checklist:

• No backwards incompatible changes were made to Ace's public interface which is defined through the main typings file (ace.d.ts) and its references:
  • https://github.com/ajaxorg/ace/blob/master/ace.d.ts
  • https://github.com/ajaxorg/ace/blob/master/ace-modes.d.ts
  • https://github.com/ajaxorg/ace/blob/master/ace-extensions.d.ts

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.92%. Comparing base (0192880) to head (3053e0d).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5626   +/-   ##
=======================================
  Coverage   86.91%   86.92%           
=======================================
  Files         594      594           
  Lines       43222    43246   +24     
  Branches     7155     7156    +1     
=======================================
+ Hits        37568    37593   +25     
+ Misses       5654     5653    -1     

Flag	Coverage Δ
unittests	86.92% <100.00%> (+<0.01%)	⬆️

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