wp_exif_date2ts throws notice on slash formatted date

[domainsupport]

When an image has an exif date in the format ...

YYYY/MM/DD HH:MM:SS

... rather than ...

YYYY:MM:DD HH:MM:SS

... which is happening more and more I have noticed, the following PHP notices are thrown ...

PHP Notice: Undefined offset: 1 in /.../wp-admin/includes/image.php on line 710
PHP Notice: Undefined offset: 2 in /.../wp-admin/includes/image.php on line 710

I think there are a lot of assumptions being made in wp_exif_date2ts() and I believe that a preg_match check like ...

<?php
if (preg_match('/^(?>\d){4}[:|\/](?>\d){2}[:|\/](?>\d){2} (?>\d){2}:(?>\d){2}:(?>\d){2}$/', $str)) {

// Process and return exif date

} else {
return false;
}

... should be done instead.

This is related to ticket 48204

Replaced wp_exif_date2ts logic with the new wp_exif_datetime function for cleaner and reusable code. Enhanced metadata to store RFC3339 formatted dates while maintaining backward compatibility. Added comprehensive PHPUnit tests for EXIF date validation and edge cases.

Fixes 48204 as well

Trac ticket: 56887

[pbearne]

This fixes https://core.trac.wordpress.org/ticket/48204 as well