\s, \S, \w, and \W in regexp

[masatake]

See #3034.

[codecov]

Codecov Report

Merging #3058 (cb537a1) into master (cab9828) will decrease coverage by 0.00%.
The diff coverage is 81.25%.

@@            Coverage Diff             @@
##           master    #3058      +/-   ##
==========================================
- Coverage   87.33%   87.32%   -0.01%     
==========================================
  Files         199      199              
  Lines       47611    47646      +35     
==========================================
+ Hits        41579    41606      +27     
- Misses       6032     6040       +8     

Impacted Files	Coverage Δ
main/lregex.c	83.54% <81.25%> (-0.06%)	⬇️
parsers/cxx/cxx_parser_function.c	92.46% <0.00%> (-0.23%)	⬇️
parsers/cxx/cxx_parser_tokenizer.c	92.45% <0.00%> (ø)

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[masatake]

I confiremd the "replacing approach" works.

[hirooih]

@masatake san,

Did you close this PR without merging intentionally?

[masatake]

This pull request was just evaluating the idea.