Fix conversion of non-utf8 sequences to AnyValue (#1253)

String values which are not valid Unicode sequences SHOULD be converted to AnyValue's bytes_value with the bytes representing the string in the original order and format of the source string.

AttributesConverter.php

@@ -46,12 +46,23 @@ public static function convertAnyValue($value): AnyValue
             $result->setDoubleValue($value);
         }
         if (is_string($value)) {
-            $result->setStringValue($value);
+            if (self::isUtf8($value)) {
+                $result->setStringValue($value);
+            } else {
+                $result->setBytesValue($value);
+            }
         }
 
         return $result;
     }
 
+    private static function isUtf8(string $value): bool
+    {
+        return \extension_loaded('mbstring')
+            ? \mb_check_encoding($value, 'UTF-8')
+            : (bool) \preg_match('//u', $value);
+    }
+
     /**
      * Test whether an array is simple (non-KeyValue)
      */