Create unicode module in datafusion/functions/src/unicode and unicode_expressions feature flag, move char_length function

[Omega359]

Is your feature request related to a problem or challenge?

As part of #9285 create a unicode module and move the char_length function to the new datafusion-functions crate in the new structure.

Describe the solution you'd like

Functions are migrated to the new crate and use the new patterns as described in #9286 & #9216

Describe alternatives you've considered

No response

Additional context

No response

[Omega359]

take