Local tasks for current route are only checked for two levels

Problem/Motivation

Drupal currently only supports two levels of local tasks because there is not recursive checking of route parents.

There is already a @todo to this effect in Drupal\Core\Menu\LocalTaskManager::getLocalTasksForRoute().

Proposed resolution

Do a recursive check on the local task 'parent_id' check rather than just checking one level of parents.

Remaining tasks

• Post patch
• Write tests