[3.3] Add Location::getFirstChild() method

[pspanja]

Lately I've seen some uses of getting the first child of a Location, implemented through the getChildren() method:

{{ location.children(1)[0].content.name }}

Method getChildren() returns an array of Location objects, intended for iteration, and using it like that is awkward and does not provide for limiting on the ContentType. For that reason I'm adding a new method on the Location object:

Location::getFirstChild(?string $contentTypeIdentifier = null): ?Location

Use from Twig:

{% set firstChild = location.firstChild('article') %}

{% if firstChild is not null %}
    {{ firstChild.content.name }}
{% endif %}

Or in redirect configuration:

ezpublish:
  system:
    frontend_group:
      ngcontent_view:
        full:
          ng_frontpage:
            temporary_redirect: '@=location.getFirstChild'
            match:
              Identifier\ContentType: ng_frontpage

[pspanja]

Thanks!