Use Sequel's ::char_length virtual function.
Use Sequel's ::char_length virtual function.

SQLite uses a different name for this function, and forcing it to
"char_length" excludes SQLite where such exclusion is not warrented,
especially given that Sequel abstracts that away.

Cf:
* https://sqlite.org/lang_corefunc.html
* http://sequel.jeremyevans.net/rdoc/classes/Sequel/SQL/Builders.html#method-i-char_length

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