#3428652 - fix js error in Date Formats machine name generation when using accented characters in label

Fixes :

• Javascript error in ajax callback for machine name generation when using non-ASCII accented chars in label (such as åäöÅÄÖš).

Adds:

• TestCase related to said characters in machine name

core/modules/system/src/Form/DateFormatFormBase.php

@@ -88,7 +88,7 @@ public function form(array $form, FormStateInterface $form_state) {
       '#default_value' => $this->entity->id(),
       '#machine_name' => [
         'exists' => [$this, 'exists'],
-        'replace_pattern' => '([^a-z0-9_]+)|(^custom$)',
+        'replace_pattern' => '[^A-Za-z0-9_]+|^custom$',
         'error' => $this->t('The machine-readable name must be unique, and can only contain lowercase letters, numbers, and underscores. Additionally, it can not be the reserved word "custom".'),
       ],
     ];