Add ancestor helper and condition.

[jordandukart]

GitHub Issue: Islandora/documentation#2071

• Other Relevant Links (Google Groups discussion, related pull requests,
  https://islandora.slack.com/archives/CM5PPAV28/p1648651493309979

What does this Pull Request do?

Adds a new condition to allow for multiple ancestors to be looked for use in context condition.
Re-works the breadcrumb builder to use the new helper to DRY things up.

What's new?

New condition.

How should this be tested?

Regression test the breadcrumb builder.

Use the condition in whatever context you want and see that it applies correctly.

Interested parties

@seth-shaw-unlv

[seth-shaw-unlv]

So, this is a bit odd, I'm not surprised that the refactor resulted in this, but we have a quirk to talk about.

At first glance, the helper works as expected. Below are sub-collection "C" before and after the PR are applied:
Original:

PR:

They look the same, which means it works. 👍

But what if we make collection "A" also a child of "C", creating a loop?
Original:

PR:

Note that the existing ancestor walking code excludes itself from the ancestor tree, whereas the PR ancestor walker includes it as the root. That may not necessarily be a bad thing, but it does break from the current implementation.

[seth-shaw-unlv]

[simonhm]

@jordandukart @seth-shaw-unlv
This condition shouldn't be required, since not all of blocks need to have this condition. You will get errors and not able to save block when not filling this condition.
It's ok with this condition left empty in Drupal 9.3.x, but not in Drupal 9.4.x-dev.

Simon.