Resolve #3487705 "Refactor banuserform"

Closes #3487705

js/private_message_ban_user_autocomplete.js

-(($, Drupal) => {
-  /**
-   * Override drupal selectHandler function
-   * @param {jQuery.Event} event The event
-   * @param {Object} ui UI
-   * @return {boolean} Members ban
-   */
-  function membersBanSelectHandler(event, ui) {
-    let valueField = $(event.target);
-    if ($(event.target).hasClass('private-message-ban-autocomplete')) {
-      const valueFieldName = 'banned_user';
-      if ($(`input[name=${valueFieldName}]`).length > 0) {
-        valueField = $(`input[name=${valueFieldName}]`);
-        // Update the labels too.
-        const labels = Drupal.autocomplete.splitValues(event.target.value);
-        labels.pop();
-        labels.push(ui.item.label);
-        event.target.value = labels.join(', ');
-      }
-    }
-    const terms = Drupal.autocomplete.splitValues(valueField.val());
-    // Remove the current input.
-    terms.pop();
-    // Add the selected item.
-    terms.push(ui.item.value);
-
-    valueField.val(terms.join(', '));
-    // Return false to tell jQuery UI that we've filled in the value already.
-    return false;
-  }
-
-  Drupal.behaviors.privateMessageBan = {
-    attach() {
-      // Attach custom select handler to fields with class.
-      $('input.private-message-ban-autocomplete').autocomplete({
-        select: membersBanSelectHandler,
-      });
-    },
-  };
-})(jQuery, Drupal);