Check if user can RemoveChildren when deleting documents from a list

After WEBUI-37, <nuxeo-delete-documents-button> was changed to use the Remove atomic permission when checking if a given document could be deleted. However, there might be a case in which the user could have this permission, but is missing the RemoveChildren permission on the parent document. Additionally, if it's a "soft delete" (to be sent to trash), the user should also have the AddChildren permission on the parent document to ensure that the documents to be deleted are properly trashed.

Ideally, we would like to only show the <nuxeo-delete-documents-button> when these conditions are satisfied, but there are several constraints:
1. <nuxeo-delete-documents-button> is aware of the list of documents to be deleted (documents), but has no reference to the parent document.
2. In the context of a search results listing, we cannot be sure that all the selected documents share the same parent document, even though the user must have RemoveChildren (and maybe AddChildren) in all of them in order to be able to perform the action.