fix: Do not render selected word markers for the same range multiple times

[andrewnester]

Issue #, if available:
#4687

Description of changes:
Avoid rendering multiple markers at the same range to avoid browser freeze when a lot of search values found in folded code.

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

[codecov]

Codecov Report

Merging #4727 (cd6ff4c) into master (f269889) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4727   +/-   ##
=======================================
  Coverage   71.15%   71.16%           
=======================================
  Files         554      554           
  Lines       55693    55698    +5     
  Branches    10421    10422    +1     
=======================================
+ Hits        39630    39635    +5     
  Misses      16063    16063           

Flag	Coverage Δ
unittests	71.16% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
lib/ace/search_highlight.js	97.22% <100.00%> (+0.44%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f269889...cd6ff4c. Read the comment docs.

[nightwing]

both calling toScreenRange, and searching for the word in a large number of lines are slow. It may be better to either use a loop skipping folded lines https://github.com/ajaxorg/ace/blob/master/lib/ace/layer/text.js#L292 or use lines data from text layer.

In the long run it may be worth to unify all these loops into something similar to getVisibleRanges of monaco.

[andrewnester]

@nightwing I don't think this CR changes how often we call toScreenRange so from this perspective it should stay the same but I agree that generally we need to revisit this and just skip folded areas