When doing bug 35919, I found that some recent change made it explode if I didn't add that include (look at the FIXME on koha-tmpl/intranet-tmpl/prog/en/modules/admin/record_sources.tt).
It is needed for the Dialog component, where we can display dates (see bug 34497)
This one might get irrelevant with Matt's work on a unified/monolithic base endpoint.