Add value format short-circuit filter

[mishterk]

In \AF_Core_Forms_Submissions::create_submission(), we make a call to acf_format_value() which formats the value for use elsewhere.

We did have a report of an issue with the ACF Extended 'Date Range Picker' field which turned out to be a bug in that field's format handler: the handler (in ACFE) wasn't set up to handle string values which was throwing errors on form submit. More info here.

Might be worth adding a short-circuit option that allows people to bypass acf_format_value() on form submission with their own handler. This would provide an isolated opportunity to cater to issues like this.