R1:e3714c86a7d5

Validate PhabricatorSearchTextField value not to be an array

Summary:
PhabricatorSearchTextField.php's parent class PhabricatorSearchField.php defines an (empty) `protected function validateControlValue($value)`.
Override this function in PhabricatorSearchTextField.php by disallowing arrays (as the only data type which cannot be casted into a text value).

Closes T15714

Test Plan: Apply D25518; then manually edit the code in `ManiphestTaskSearchEngine.php` by defining an array and passing that array to…