chore: small type fixes

[akoreman]

Issue #, if available: NA

Description of changes:

• mark event as optional in endOperation to be inline with the previously defined types.
• mark config as optional in the contstructor of SyntaxMode.HighlightRules to be inline with the previously defined types.
• Expose $onChange and $syncOptions from SearchBox to expose these methods to users building custom search boxes based on the SearchBox implementation.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

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

[github-actions]

One of the public type files has been updated, plase make sure there are no backwards incompatible changes done in the PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.02%. Comparing base (3eaf667) to head (0c5dc55).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5690   +/-   ##
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  Coverage   87.02%   87.02%           
=======================================
  Files         598      598           
  Lines       43588    43588           
  Branches     7162     7162           
=======================================
  Hits        37932    37932           
  Misses       5656     5656           

Flag	Coverage Δ
unittests	87.02% <ø> (ø)

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