Fix EZP-22387: Error rendering a page block with trashed content

Link: https://jira.ez.no/browse/EZP-22387

## Description
Items located in the trash are returned as valid content by ezpage. In order to avoid that, we are making sure items returned are available in `ezcontentobject_tree`.

It only makes it a closer match to the legacy SQL request from ezflow:
https://github.com/ezsystems/ezflow/blob/483e6ddfb13251eb2b2841edbfde14e069b27236/packages/ezflow_extension/ezextension/ezflow/classes/ezflowpool.php#L96

Invalid items will then be cleared by cronjob:
```
php ezpublish/console --env=prod ezpublish:legacy:script runcronjobs.php ezflow-cleanup
```

## Test
Manual tests.