Resolve @todo in OffCanvasTestBase::assertAllContextualLinksLoaded

Problem/Motivation

\Drupal\Tests\system\FunctionalJavascript\OffCanvasTestBase::assertAllContextualLinksLoaded has the following comment:

@todo Move this function to https://www.drupal.org/node/2821724.

But #2821724: Create Javascript Tests for Contextual Links → is resolved and the function still exists.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet