Move from_unixtime, now, current_date, current_time functions to datafusion-functions

[Omega359]

Is your feature request related to a problem or challenge?

As part of #9285 the remaining datetime functions should be migrated 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

[Omega359]

I think for the now, current_date and current_time functions I'll need #9304 to be merged before those functions can be migrated as they do not work in the same way as normal functions (the value is chosen during planning, not execution)