Enhancement: support Merge Tag modifiers for all date fields

[rafaehlers]

At this moment, you can only format date from the {date_created} Merge Tag. It will be amazing if we can use those modifiers to modify any other date field merge tag as well.

Related: https://docs.gravityview.co/article/331-date-created-merge-tag

Example usage: {My Date field:1:format:m/d/Y}

This is requested often by our users.

[rafaehlers]

https://secure.helpscout.net/conversation/1078952864/25213/

[rafaehlers]

https://secure.helpscout.net/conversation/1666787977/37566

[rafaehlers]

Suggestion: https://gravitywiz.com/gravity-forms-date-merge-tags/

[zackkatz]

Check out GF_Field_Date::get_output_date_format() in gravityforms/includes/fields/class-gf-field-date.php

[zackkatz]

@rafaehlers Please review to see if this is closed. If so, please close and notify.

[rafaehlers]

Almost ready:

• Add support for :human merge tag modifiers on all Date fields #1990
• Add merge tags {now} {today} {yesterday}
• Create new doc explaining all of these
• Add the :format modifier to time fields