Unify download permissions and action filter

NXP-17933 added file security policies based on JavaScript evaluation (https://doc.nuxeo.com/nxdoc/file-download-security-policies/). This would be useful also for standard action filters (https://doc.nuxeo.com/nxdoc/filters-and-access-controls/).

Conversely, file security policies would benefit from being expressible using standard action filters.