Provide breadcrumb submodule

Looking good

1. +++ b/entity_hierarchy_breadcrumb/src/HierarchyBasedBreadcrumbBuilder.php
   @@ -0,0 +1,213 @@
   +  /**
   +   * The parent candidate service.
   +   *
   +   * @var \Drupal\entity_hierarchy\Information\ParentCandidateInterface
   +   */
   +  protected $parentCandidate;
   ...
   +   * @param \Drupal\entity_hierarchy\Information\ParentCandidateInterface $parent_candidate
   +   *   The parent candidate service.
   ...
   +    $this->parentCandidate = $parent_candidate;
   

   Not used anymore?

2. +++ b/entity_hierarchy_breadcrumb/src/HierarchyBasedBreadcrumbBuilder.php
   @@ -0,0 +1,213 @@
   +    // TODO: Should we handle multiple fields??
   ...
   +      // TODO: Config option?
   ...
   +    // TODO: Config option?
   

   If people don't like the defaults, they can implement their own extending from this one.

   Happy to leave it as is.

3. +++ b/entity_hierarchy_breadcrumb/src/HierarchyBasedBreadcrumbBuilder.php
   @@ -0,0 +1,213 @@
   +  private function getEntityFromRouteMatch(RouteMatchInterface $route_match) {
   ...
   +  private function getHierarchyFieldFromEntity(ContentEntityInterface $entity) {
   

   Lets make these protected in case someone wants to do something about multiple fields that is specific to their use-case - they can then extend

4. +++ b/entity_hierarchy_breadcrumb/tests/src/Kernel/BreadcrumbTest.php
   @@ -0,0 +1,123 @@
   +    $this->testRoute = new Route('/entity_test/{entity_test}', [], [], ['parameters' => [static::ENTITY_TYPE => ['type' => 'entity:' . static::ENTITY_TYPE]]]);
   

   I think this will break phpcs