Entity parameter fallbacks for "current entity for page" as a hook

[e0ipso]

Problem

We have this line in our code:

https://github.com/Lullabot/ph_tools/blob/main/src/PageService.php#L81

    // @todo: turn this into a hook!
    $entity_parameter = $route_match->getParameter($entity_type_id) ?? $route_match->getParameter('current_entity');
    $entity_preview_parameter = $route_match->getParameter($entity_type_id . '_preview');

    if ($entity_parameter) {
      $entity = $entity_parameter;
    }
    if ($entity_preview_parameter) {
      $entity = $entity_preview_parameter;
    }

Note the 'current_entity' custom parameter. This comes from the Bravo project and it should be made generic.

Proposed solution

Let's introduce a hook that can be used by sites to derive the entity parameter.

    $entity_parameter = $route_match->getParameter($entity_type_id);
    $this->moduleHandler->hookAlter($entity_parameter);