Editorial: consider linking "present" consistently

[annevk]

Instead of present use <a for="dictionary member">present</a>. However, maybe this isn't worth it if dictionaries get recast as Infra maps so we'd have to use maps infrastructure instead...

[domenic]

They already are mapped, aren't they? So we can do x["y"] exists.

[annevk]

@domenic hmm yeah, maybe we should update https://heycam.github.io/webidl/#idl-dictionaries to encourage the new terminology then?

[domenic]

Yeah probably a good idea. Might want to add some stuff to Infra so that any links to "present" get redirected there.