refactor: PHP 8.5 language features via Rector

rector.php gets the PHP sets up to 8.5. Mostly constructor promotion with
readonly properties, typed class constants, ??=, arrow functions,
str_contains/str_starts_with, catch without unused variables, array_any
and #[\Override] on overridden properties; array_key_exists() keys are
cast to string (null keys are deprecated in PHP 8.5). Long promoted
constructor signatures are wrapped one parameter per line.

Checked locally: a crawl of ~1,900 frontend URLs over all sites and the
backchannel APIs (/api/hotel, /api/product, content feed manifest and
records of every type) render the same as before.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/ep_theme/Classes/Form/AbstractMappedFinisher.php

@@ -46,7 +46,7 @@ abstract class AbstractMappedFinisher extends AbstractFinisher
         $formValues = $this->finisherContext->getFormValues();
 
         foreach ($this->parseMapping() as $remote => $local) {
-            if (false === array_key_exists($local, $formValues)) {
+            if (false === array_key_exists((string) $local, $formValues)) {
                 continue;
             }
 
@@ -130,13 +130,13 @@ abstract class AbstractMappedFinisher extends AbstractFinisher
         if ($value instanceof FileReference) {
             $resource = $value->getOriginalResource();
 
-            return null !== $resource ? $resource->getName() : null;
+            return $resource?->getName();
         }
 
         if (true === is_object($value)) {
             $this->logWarning('Form value skipped while collecting labeled values: unsupported type.', [
                 'element' => $identifier,
-                'class' => get_class($value),
+                'class' => $value::class,
             ]);
 
             return null;