Start using the Infra Standard

[domenic]

See https://blog.whatwg.org/infra for background. Let's use this issue to track the changes we'll want to make to HTML. I anticipate us doing so over the course of several PRs, as the data structures especially might require some back and forth (e.g. adding missing things to Infra for manipulating them).

• Overall integration
  • Add to the kitchen sink diagram, maybe? It's also missing Fetch, and is getting crowded.
  • Add a prominent "HTML depends on the Infra Standard" somewhere early; maybe in the beginning of 2. Common infrastructure, before 2.1. Terminology?
  • Add an appropriate section with dfn cross references to Dependencies; probably before anything else
• Removal of now-redundant things
  • Remove byte sequences from typographic conventions
  • Remove the definition of "or" from Terminology
  • Remove all of case-sensitivity and string comparison. I guess we need to move "prefix match" into Infra.
  • Remove most of the character classes defined in common parser idioms
  • Remove conformance requirements. Maybe we want to move its example into Infra.
  • Remove Namespaces but move its user agent note somewhere else, probably (maybe the XML section)
• Data structure usage (not complete, update as we find more...)
  • module map
  • CustomElementRegistry (kind of a strange case)
  • when-defined promise map
  • custom element reaction queue
  • custom element reactions stack
  • element queue
  • backup element queue

[domenic]

I'm happy with our current strategy of upgrading as we go; we don't need a separate tracking issue for this.