Revert multiline toggle-comment behavior

[bobbylight]

The prior fix for #570 (f0d8326) accidentally broke behavior when multiple lines are selected. Specifically, in that case we should continue to toggle the "commented out" state for all lines uniformly, based on whether they are all currently commented out or not. This is needed to uniformly comment out blocks of code even if they have line comments in them.

This PR reverts to the prior behavior there, but keeps the prior fix's behavior change for toggling single-line comments (i.e. leading whitespace is ignored in the check). Unit tests have been thoroughly improved to cover all cases.

[codecov]

Codecov Report

Attention: Patch coverage is 73.33333% with 16 lines in your changes missing coverage. Please review.

Project coverage is 80.40%. Comparing base (f0d8326) to head (947005e).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...e/ui/rsyntaxtextarea/RSyntaxTextAreaEditorKit.java	73.33%	5 Missing and 11 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #591      +/-   ##
============================================
- Coverage     80.40%   80.40%   -0.01%     
+ Complexity     7793     7792       -1     
============================================
  Files           178      178              
  Lines         30261    30261              
  Branches       3914     3913       -1     
============================================
- Hits          24332    24330       -2     
- Misses         4255     4257       +2     
  Partials       1674     1674              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[bobbylight]

This is in the latest 3.5.4-SNAPSHOT on Sonatype.