[PP-1] Add `JsComponent` unit test

Actually \Drupal\Tests\experience_builder\Kernel\Plugin\ExperienceBuilder\ComponentSource\JsComponentTest already exists!

Wait for 📌 Expand `::getClientSideInfo()` test to all ComponentSource plugins Active and 📌 ComponentSource robustness: add `ComponentSourceTestBase::testSettings()` Active , ideally, but not necessarily.