Use RootedJsonData for validation in metastore service

[dafeder]

Code to be adjusted:

• [x] metastore_search. Facets adjusted to RootedJsonData
• [x] Drupal\Tests\metastore_search\Unit\SearchTest
• [x] Drupal\Tests\metastore_search\Unit\Plugin\search_api\datasource\DkanDatasetTest::test
• [x] Drupal\Tests\datastore\Service\ResourcePurgerTest
• [x] Drupal\Tests\harvest\Load\DatasetTest
• [x] Drupal\Tests\json_form_widget\Unit\SchemaUiHandlerTest
• [ ] Consider using RootedJsonData in Storage 'retrieve'-like methods

Estimate: 1 day

[ghost]

Nikolay expects this to be done in 2 days.

[ghost]

Nikolay should put this ticket aside and help Riadh with metastore work (Chadia and Susana will assign him the tickets), then review testing on #3372 with Dan after he comes back from vacation.

[ghost]

@sussimsua Removing this from our Support board as well.