feat: show 2 context characters of a line when moving to it

[andredcoliveira]

Issue #, if available: N/A

Description of changes:

• When moving from one line to a shorter line that is hidden, the content is scrolled to exactly the cursor position, showing no characters at all from that line, which is a less than optimal UX. This change makes it so the content is scrolled to show a couple of characters from that line.
• I've included an automated test
  • It only covers LTR, but I've manually tested in RTL too

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

Base: 86.09% // Head: 86.10% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (425732d) compared to base (6fb39e3).
Patch coverage: 85.71% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4998      +/-   ##
==========================================
+ Coverage   86.09%   86.10%   +0.01%     
==========================================
  Files         546      546              
  Lines       41568    41588      +20     
  Branches     6551     6552       +1     
==========================================
+ Hits        35788    35810      +22     
+ Misses       5780     5778       -2     

Flag	Coverage Δ
unittests	86.10% <85.71%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
src/virtual_renderer.js	79.64% <76.00%> (+0.27%)	⬆️
src/virtual_renderer_test.js	99.07% <100.00%> (+0.07%)	⬆️

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