Following a chat between the Performance Team and Microsoft Edge developers, we should consider changing our use of Link preconnect to emit a header instead of the <link> element because Edge only supports the header variant, not the <link> element variant yet.
Other browsers supporting preconnect support both, so switching should be uncontroversial.
This task is for tracking any use of preconnect Link tags in MediaWiki-related code as deployed by Wikimedia.