[11.x] Stringable is also an interface of symfony (#51309)

* filled and blank works with `Stringable`

* unnecessary

* `Stringable` is also an interface from symfony and is implemented on models. So if we check a model if a model is filled it except an error: Call to undefined method App\\Model::trim(). So we use now explicit Illuminate\Support\Stringable

* reduce compare to native trim - function

* unnused Model

---------

Co-authored-by: stefan.riedel <stefan.riedel@arbeitsmedizin.de>

src/Illuminate/Support/helpers.php

@@ -61,7 +61,7 @@ function blank($value)
         }
 
         if ($value instanceof Stringable) {
-            return $value->trim()->toString() === '';
+            return trim((string) $value) === '';
         }
 
         return empty($value);