docs: modernize classes in code snippets

[GeorgeSapkin]

I've changed a few code snippets in the docs to use the modern class syntax. I've only touched the English bits for now.

[Trott]

@nodejs/documentation

[Trott]

I know this unfortunately got ignored for a long time, but any chance it can be rebased to resolve the conflicts?

@nodejs/website Reviews for this would be good.

[Trott]

@nodejs/domains @nodejs/website This could use a few more reviews.