Previously, some methods handled items/lists with multiple allowed names,
and some only allowed a single name. As the overhead of always handling
multiple names isn't that large, do that everywhere and make the overall
API more streamlined in the process.
These optimize out unnecessary code duplication, reserve vector capacity beforehand by leveraging `Iterator`s and avoid unnecessary double-lookups into HashMaps.
Reviewed-on: https://codeberg.org/topola/topola/pulls/128
Co-authored-by: Alain Emilia Anna Zscheile <fogti+devel@ytrizja.de>
Co-committed-by: Alain Emilia Anna Zscheile <fogti+devel@ytrizja.de>