N°6414 Move existing AbstractSimpleField::Validate impl to custom validators

- LinkedSetField
- SelectObjectField
- MultipleChoicesField (warning this hierarchy contains non multiple value fields like SelectField !)

Also change AbstractValidator::Validate signature : now we are returning an array of error messages, so that we can return multiple ones

sources/Form/Field/Field.php

@@ -505,15 +505,33 @@ abstract class Field
 		return $this;
 	}
 
+	/**
+     * @param string $sValidatorClassName validator class name, should be one of {@see AbstractValidator} children
+     * @return $this
+     * @since 3.1.0 N°6414
+     */
+    final public function RemoveValidatorsOfClass(string $sValidatorClassName)
+    {
+        foreach ($this->aValidators as $iKey => $oValue) {
+            if ($oValue instanceof $sValidatorClassName) {
+                unset($this->aValidators[$iKey]);
+            }
+        }
+
+        return $this;
+    }
+
 	/**
 	 * Note : Function is protected as aErrorMessages should not be add from outside
 	 *
 	 * @param string $sErrorMessage
+	 *
 	 * @return $this
 	 */
 	protected function AddErrorMessage(string $sErrorMessage)
 	{
 		$this->aErrorMessages[] = $sErrorMessage;
+
 		return $this;
 	}