doc: normalize Markdown code block info strings

Prior to this commit, Markdown fenced code blocks in Markdown
files had inconsistent info strings. This has been corrected to
standardize on the one shown in the CommonMark spec.

Refs: https://github.com/commonmark/commonmark-spec/blob/1103710025f340702edcb070be41f9982b6544d5/spec.txt#L131

PR-URL: https://github.com/nodejs/node/pull/33542


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>