Entity type helper method to determine if the entity ID is integer

A new EntityTypeInterface helper method has been introduced that allows to check if the entity ID is an integer. This was necessary because we are doing this check in a lot of point in the site...

  /**
   * Checks if this entity type has an integer ID.
   *
   * @return bool|null
   *   Returns:
   *     - TRUE if the entity type ID is defined as integer;
   *     - FALSE if the entity type ID is defined as string;
   *     - NULL if the entity type lacks an ID key.
   */
  public function hasIntegerId(): ?bool;

Other changes:

• DefaultHtmlRouteProvider::getEntityTypeIdKeyType() is deprecated. Even this is a protected method, there is a big chance that it's used by 3rd-parties extending DefaultHtmlRouteProvider, so we prefer to deprecate it instead of a simple remove.
• \Drupal\comment\CommentTypeForm::entityTypeSupportsComments() is deprecated.
• _comment_entity_uses_integer_id() is deprecated