fix: api form submission, files correctly return array

Because we want to use the property parameter correctly

for getting the id of the first file it should be ?property=[files][0][id]
before this fix, files is an object and the property needs to be [files][0].id

EMS/submission-bundle/src/Entity/FormSubmission.php

@@ -144,7 +144,8 @@ public function toArray(): array
         }
 
         if ($this->files->count() > 0) {
-            $data['files'] = $this->files->toArray();
+            $files = $this->files->toArray();
+            $data['files'] = \array_map(static fn (FormSubmissionFile $f) => $f->toArray(), $files);
         } else {
             unset($data['files']);
         }

EMS/submission-bundle/src/Entity/FormSubmissionFile.php

@@ -93,6 +93,14 @@ public function __construct(/**
      * @return array<string, mixed>
      */
     public function jsonSerialize(): array
+    {
+        return $this->toArray();
+    }
+
+    /**
+     * @return array<string, mixed>
+     */
+    public function toArray(): array
     {
         return [
             'id' => $this->id->toString(),