move strpos, substr functions to datafusion_functions #9835

Is your feature request related to a problem or challenge?

As part of #9285 move the strpos and substr functions 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