Fix date formatting

Hey there,

I'm having the issue that my date-time-picker field jumps back in time on each update of the post.
A solution I found that's working for me is to change the line 3879 in /includes/api/api-helpers.php (https://github.com/AdvancedCustomFields/acf/blob/master/includes/api/api-helpers.php#L3871):

// includes/api/api-helpers.php:3871
return wp_date($format, $unixtimestamp);

I also found this post by the WordPress core team:
https://make.wordpress.org/core/2019/09/23/date-time-improvements-wp-5-3/

Not recommended

• don’t localize time based on WP timestamp:
  • date_i18n( DATE_RFC3339, $timestamp + $offset )

Recommended

• localize time based on Unix timestamp:
  • wp_date( DATE_RFC3339, $timestamp )

Changing return date_i18n( $format, $unixtimestamp ); to return wp_date($format, $unixtimestamp); resolves the problem and is recommended by WordPress. Can this be fixed, please?

Start at includes/api/api-helpers.php around line 3871 and inspect the date-formatting call alongside the WordPress date-time guidance linked in the issue. Verify that the date-time-picker no longer jumps backward after a post update; no test file is named in the payload.