Add method to EntityRepository to load multiple entities by UUID

Changes look good to me, also I think it is a good idea to add this ability to load multiple entities by UUID. Hope it will be added in the nearest future.

The only thing that should be fixed is "ore", should be "or" in EntityRepositoryInterface.php line 31.

Fixed typo

Tests fail because of:

1) Drupal\Tests\system\Functional\Module\InstallUninstallTest::testInstallUninstall
PHPUnit\Framework\Exception: Fatal error: Declaration of Drupal\Core\Entity\EntityRepository::loadEntitiesByUuids(string $entity_type_id, array $uuids): array must be compatible with Drupal\Core\Entity\EntityRepositoryInterface::loadEntitiesByUuids($entity_type_id, $uuids): array in /var/www/html/core/lib/Drupal/Core/Entity/EntityRepository.php on line 64

Updated the patch to fix the error.

When fixing the issue of #7, i noticed that, loadByProperties for field_config cannot take array of values.

Observation:
In FieldConfigStorage.php, line number 141 the foreach statement cannot take multiple array of uuid values. So I think we need to individually pass uuid value to loadByProperties method in EntityRepository class

Please check and let me know if I have analysed correctly.

Thanks

May be below one would be helpful.

Fixing test case failure

+++ b/core/lib/Drupal/Core/Entity/EntityRepository.php
@@ -54,15 +54,28 @@ public function __construct(EntityTypeManagerInterface $entity_type_manager, Lan
     }
-
-    $entities = $this->entityTypeManager->getStorage($entity_type_id)->loadByProperties([$uuid_key => $uuid]);
-
-    return ($entities) ? reset($entities) : NULL;
+    $entities = [];
+    foreach ($uuids as $ukey => $uuid_value) {
+      $uuid_key_value = [];
+      $entities_by_id = $this->entityTypeManager->getStorage($entity_type_id)->loadByProperties([$uuid_key => $uuid_value]);
+      $uuid_key_value = array_keys($entities_by_id);
+      if (isset($uuid_key_value[0])) {
+        $entities[$entities_by_id[$uuid_key_value[0]]->uuid()] = $entities_by_id[$uuid_key_value[0]];
+      }

this implementation actually doesn't make it more efficient at all. I see that it was done above due to a problem with config entities. We could try if an entity query works better, but it's already transformed to that internally anyway. Last resort would be to only do a bulk load for content entities, but without doing that, this IMHO is pointless and doesn't provide any improvement compared to just calling loadEntityByUuid() in a loop.

To fix #13, the for loop should be replaced with sth like:

$entities = $this->entityTypeManager->getStorage($entity_type_id)->loadByProperties([$uuid_key => $uuids]);