Trashed folder allows document creation

Reproductible on nightly.nuxeo.com.

1. create a folder
2. create a note inside it
3. trash the folder
4. go to the trash
5. navigate to the trashed folder
6. observe the button (plus sign) is available for creating documents (see possiblecreation.png)
7. create a note
8. observe the note is neither visible in the trashed folder or the untrashed workspace parent
9. now untrash the folder
10. observe the created note is now visible

This is an inconsistent behavior. The document creation button should not be available when browsing trashed documents to avoid such issues. Maybe this should be dealt à the core level to prevent any document creation when the parent document has the ecm:isTrashed flag set.

I let the platform decide on what is best.