MDL-58859 mlbackend_php: Added to core

Part of MDL-57791 epic.

lib/mlbackend/php/phpml/src/Phpml/Exception/NormalizerException.php

@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Phpml\Exception;
+
+class NormalizerException extends \Exception
+{
+    /**
+     * @return NormalizerException
+     */
+    public static function unknownNorm()
+    {
+        return new self('Unknown norm supplied.');
+    }
+}