Use multibyte-aware trimming by default #137

Multibyte mode was added to Trim, LeftTrim, RightTrim and ToArrayOfStrings attributes and their resolvers in #131. It's disabled by default to keep backward compatibility.

Most of the input in modern web applications is UTF-8, so multibyte-aware trimming is the expected behavior in most cases. The default value of the multibyte parameter in the resolvers should be changed
to true.

To do:

• Change the default value of multibyte to true in TrimResolver, LeftTrimResolver, RightTrimResolver and ToArrayOfStringsResolver.
• Throw LogicException when multibyte is true, but the required mb_* functions aren't available.
• Update PHPDoc and docs/guide/en/typecasting.md.
• Add an upgrade note.

⚠️ Don't implement it before start version 2.0 development