[REF] extract prepareCreate from CustomField.create

[eileenmcnaughton]

Overview

Straight forward extraction - cleaning up code with a view to offering a more efficient wrapping function

Before

Code less readable

After

Code more readable

Technical Details

Comments

[civibot]

(Standard links)

• If this is your first pull-request for CiviCRM, please browse CONTRIBUTING.md for information about the development and testing processes.
• If you are reviewing this pull-request, you may wish to consult the test sites and the Review Standards (long template, short template).

[eileenmcnaughton]

@colemanw any chance you can check this - can trade review

[monishdeb]

Tested working fine. Nice code extraction :)