Issue #2360647 by quietone, alexpott, Manuel Garcia, jhodgdon: Documentation...

 * dependencies. Implementations should call the base class implementation to

 * inherit the generic functionality.

 *

 * Classes for configurable plugins are a special case. They can either declare

 * their configuration dependencies using the calculateDependencies() method

 * described in the paragraph above, or if they have only static dependencies,

 * these can be declared using the 'config_dependencies' annotation key.

 * Some configuration entities have dependencies from plugins and third-party

 * settings; these dependencies can be collected by

 * \Drupal\Core\Config\Entity\ConfigEntityBase::calculateDependencies().

 * Entities with third-party settings need to implement

 * \Drupal\Core\Config\Entity\ThirdPartySettingsInterface in order to trigger

 * this generic dependency collection. Entities with plugin dependencies need to

 * implement \Drupal\Core\Entity\EntityWithPluginCollectionInterface; this

 * causes the base calculateDependencies() method to add the plugins' providers

 * as dependencies, as well as dependencies declared in the

 * "config_dependencies" key from the plugins' definitions. In addition, plugins

 * that implement \Drupal\Component\Plugin\ConfigurablePluginInterface can

 * declare additional dependencies using

 * \Drupal\Component\Plugin\DependentPluginInterface::calculateDependencies(),

 * and these will also be collected by the base method.

 *

 * If an extension author wants a configuration entity to depend on something

 * that is not calculable then they can add these dependencies to the enforced

 * @see \Drupal\Core\Config\Entity\ConfigEntityInterface::getDependencies()

 * @see \Drupal\Core\Config\Entity\ConfigEntityInterface::onDependencyRemoval()

 * @see \Drupal\Core\Config\Entity\ConfigEntityBase::addDependency()

 * @see \Drupal\Core\Config\Entity\ConfigEntityBase::calculateDependencies()

 * @see \Drupal\Core\Config\ConfigInstallerInterface::installDefaultConfig()

 * @see \Drupal\Core\Config\ConfigManagerInterface::uninstall()

 * @see \Drupal\Core\Config\Entity\ConfigEntityDependency