Better checking for duration_field that handles 8.x-2.x-dev + git checkouts

Problem/Motivation

Follow-up to #3061411: Hide the daterange_duration widget if the right version of duration_field isn't installed:

If you have a git checkout of duration_field or use the 8.x-2.x-dev release, this code fails:

 try {
    $duration_field_info = \Drupal::service('extension.list.module')->getExtensionInfo('duration_field');
    if (version_compare($duration_field_info['version'], '8.x-2.0-rc2', '<')) {
      // If we don't have 8.x-2.0-rc2 or later, hide the widget.
      unset($info['daterange_duration']);
    }
  }
  catch (UnknownExtensionException $e) {
    // Also hide the widget if there is no duration_field module at all.
    unset($info['daterange_duration']);
  }

version_compare() is confused with "8.x-2.x-dev", the code thinks we don't have a working version of duration_field, and we hide the plugin unnecessarily. This causes tests to fail if you're running in an environment with git checkouts.

Proposed resolution

Instead of trying to directly inspect version numbers, let's just make sure one of the methods we need from one of the duration_field service classes is_callable().

Remaining tasks

1. Do it.
2. Watch testbot still pass.
3. Peer review?
4. Commit.

User interface changes

API changes

Data model changes

Release notes snippet