fix: allow setting the placeholder type for nls

[akoreman]

Issue #, if available: NA

Description of changes: Follow-up to #5581, when setting the translated messages, allow configuring which placeholder is used for parameters. The allowed options are dollar signs or curly brackets. Default to dollar signs to not break current behavior.

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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 86.78%. Comparing base (6e217a7) to head (93ac44c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5584   +/-   ##
=======================================
  Coverage   86.78%   86.78%           
=======================================
  Files         594      594           
  Lines       43020    43033   +13     
  Branches     7129     7132    +3     
=======================================
+ Hits        37334    37347   +13     
  Misses       5686     5686           

Flag	Coverage Δ
unittests	86.78% <100.00%> (+<0.01%)	⬆️

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