A better solution would be to add ATTACHMENT_VIEW, ATTACHMENT_DELETE,
ATTACHMENT_CREATE and ATTACHMENT_ADMIN permissions and create a
`LegacyAttachmentPolicy` `IPermissionPolicy` implementation (enabled by
default). This implementation would effectively implement the
behaviour of _perm_maps - that of mapping ATTACHMENT_* checks to the
appropriate legacy permission (eg. ATTACHMENT_VIEW in the context of
wiki:WikiStart would be mapped to WIKI_VIEW, etc.).