[DOCTRINE][SCHEMADEF] Create a new metadata driver to allow us to continue using static schemaDef functions

This has the benefit of requiring fewer code changes, as well as providing a better isolation
between GNU social and symfony, useful in case the framework needs to be changed

src/Util/SchemaDefDriver.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace App\Util;
+
+use Doctrine\Persistence\Mapping\ClassMetadata;
+use Doctrine\Persistence\Mapping\Driver\StaticPHPDriver;
+
+class SchemaDefDriver extends StaticPHPDriver
+{
+    public function loadMetadataForClass($className, ClassMetadata $metadata)
+    {
+        $schema = $className::schemaDef();
+        $metadata->addField($schema[0]);
+    }
+}