EPUB: support multiple publishers

This also fixes https://github.com/johnfactotum/foliate/issues/1633

epub.js

@@ -267,7 +267,7 @@ const getMetadata = opf => {
         subtitle: dc.title?.find(x => prop(x, 'title-type') === 'subtitle')?.value,
         language: dc.language?.map(x => x.value),
         description: one(dc.description),
-        publisher: makeContributor(dc.publisher?.[0]),
+        publisher: dc.publisher?.map(makeContributor),
         published: dc.date?.find(x => x.attrs.event === 'publication')?.value
             ?? one(dc.date),
         modified: one(properties[PREFIX.dcterms + 'modified'])