fix deleted objects are not handled at all

[rliebi]

Right now deleted objects are not removed from index. This fix allows to process deleted objects as well and remove them from index.

[limenet]

Disregard, I forgot getById() returns null instead of throwing

Not entirely certain but I think \Valantic\ElasticaBridgeBundle\Messenger\Handler\AbstractRefreshHandler::resolveElement also needs a fix in the try-catch as the handler might be executed (much) later and getById will fail and the part in lines 28 ff which is supposed to handle that, is skipped because of the exception that's thrown above it.

try {
    $element = $className::getById($message->id);
} catch (\Throwable) {
    throw new PimcoreElementNotFoundException($message->id, $message->className);
}

if (!$element instanceof AbstractElement) {
    // The element in question was deleted so we need a skeleton.
    // ...
}