Fix multiselect/checkbox custom field defaults on registration profile

[colemanw]

Overview

Fixes a bug where certain types of custom fields were not being correctly pre-populated on event registration profiles.

To Reproduce

1. Create a checkbox or multiselect custom field for contacts.
2. Add it to a profile.
3. Add the profile to an event registration page.
4. Edit your own contact record and fill in some values for that field.
5. Visit the event registration form. Observe the field is not pre-populated with the expected value (while other fields on the form have been correctly filled-in).

Technical Details

The CRM_Core_BAO_UFGroup::setProfileDefaults() function expects each field to be an array,
but this function was just passing it the number 1. So it did not have enough field metadata
to correctly format each value.

Comments

This touches toxic code so this is a minimal bugfix; however additional cleanup and refactoring is needed.

[civibot]

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[colemanw]

@pradpnayak please review

[pradpnayak]

This is now working on Event registration page but not for Contribution page.

[pradpnayak]

@colemanw have submitted #16991 to fix on contribution online page

[pradpnayak]

good to merge!