feat: update mouse selection at user's refresh rate

[thennothinghappened]

Issue #, if available: #5716

Description of changes:
Rather than updating the mouse selection at a fixed interval of 20 milliseconds, I've changed it to use event.nextFrame(), which calls requestAnimationFrame(). This means that user selection is updated at their refresh rate, and thus results in a much smoother experience; this is especially noticeable on (but not limited to) high refresh-rate monitors.

I did note that there are many places within Ace where this fixed magic number of 20 is used, rather than hooking into the animation loop - these could also be made smoother by making similar adjustments.

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.02%. Comparing base (ef08dfb) to head (514ef45).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5717   +/-   ##
=======================================
  Coverage   87.02%   87.02%           
=======================================
  Files         598      598           
  Lines       43593    43598    +5     
  Branches     7163     7164    +1     
=======================================
+ Hits        37936    37941    +5     
  Misses       5657     5657           

Flag	Coverage Δ
unittests	87.02% <100.00%> (+<0.01%)	⬆️

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