Check for Event createInstances too soon

Problem/Motivation

DisplayBuilderEventsSubscriber::dispatchToIslands() creates instances before filtering to keep enabled instances only.

    $islands = $this->islandManager->createInstances($this->islandManager->getDefinitions(), $contexts, $configuration);

    $island_enabled = $event->getEnabledIslands();
    $visible_islands = $event->getVisibleIslands();

    foreach ($islands as $island_id => $island) {
      if (!isset($island_enabled[$island_id])) {
        continue;
      }

Proposed resolution

Filter the definitions before instantiating:

$definitions = \array_intersect_key($this->islandManager->getDefinitions(), $island_enabled);
$islands = $this->islandManager->createInstances($definitions, $contexts, $configuration);

Remaining tasks

User interface changes

API changes

Data model changes