Issue #3323855 by benjifisher: Improve class comment for Drupal\Core\Menu\MenuLinkTreeElement

/**

 * Provides a value object to model an element in a menu link tree.

 *

 * \Drupal\Core\Menu\MenuLinkTreeElement objects represent a menu link's data.

 * Objects of this class provide complimentary data: the placement in a tree.

 * \Drupal\Core\Menu\MenuLinkInterface objects represent a menu link's data.

 * Objects of this class provide complementary data: the placement in a tree.

 * Therefore, we can summarize this split as follows:

 * - Menu link objects contain all information about an individual menu link,

 *   plus what their parent is. But they don't know where exactly in a menu link

 *   tree they live.

 * - Instances of this class are complimentary to those objects, they know:

 * - Instances of this class are complementary to those objects, they know:

 *   - All additional metadata from {menu_tree}, which contains "materialized"

 *     metadata about a menu link tree, such as whether a link in the tree has

 *     visible children and the depth relative to the root.