Merge branch '4.4' into 5.4

* 4.4:
  Fix composer on appveyor
  [PropertyAccess] Fix typo in PropertyAccessor::readProperty() DocBlock
  [VarExporter] Fix exporting objects with readonly properties
  [ExpressionLanguage] Fix matches when the regexp is not valid
  [Messenger] Add mysql indexes back and work around deadlocks using soft-delete
  [Validator] Fix File constraint invalid max size exception message
  [Console] Fix exit status on uncaught exception with negative code

PropertyAccessor.php

@@ -443,7 +443,7 @@ private function readIndex(array $zval, $index): array
     }
 
     /**
-     * Reads the a property from an object.
+     * Reads the value of a property from an object.
      *
      * @throws NoSuchPropertyException If $ignoreInvalidProperty is false and the property does not exist or is not public
      */