Add video duration for field mapping

This adds some of the basic structure necessary, now to work out how to actually have the video's duration as an available value.

Rerolled for 10.2, for anyone who wants to test it.

This uses getID3 to get the duration in seconds, which are rounded to the nearest second.

It might be worth spinning this off as a separate contrib module that replaces core's standard VideoFile plugin with its own and then adds all of the getID3 attributes.

A bare version of #4 for loading via composer.

The Needs Review Queue Bot → tested this issue.

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I realized that it needed to check the parent plugin for possible attributes if the known one wasn't found.

Minor mistake on the 10.2 patch.

FYI I formatted the timestamp like this:

/**
 * Implements hook_preprocess_field() for "field_duration".
 */
function MYMODULE_preprocess_field__field_duration(array &$variables) {
  // Reformat the duration as a time string.
  foreach ($variables['items'] as $key => $item) {
    $duration = trim($item['content']['#markup']);
    $minutes = floor($duration / 60);
    $seconds = $duration - ($minutes * 60);
    $variables['items'][$key]['content']['#markup'] = $minutes . ':' . $seconds;
  }
}

Hi, I merely glanced at the patch and saw the constant and I recalled there is a standard for naming. So, I am linking that here, https://www.drupal.org/docs/develop/standards/php/php-coding-standards#s... → . I think the name needs to change.

Rerolled the bare patch for the latest 10.3.

The standards don't really differentiate between global constants vs class constants, so I don't think it's necessary for class constants to be prefixed with the module's name as they are only available within that class? If I'm wrong on that then I'm happy to update it.