doc: standardize constructor doc header layout

Our docs use a mixture of _Constructor: `new Fhqwhgads()`_ in some
headers and only _`new Fhqwhgads()`_ in other headers. The latter is
about three times as common, so let's standardize on that.

PR-URL: https://github.com/nodejs/node/pull/33781


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>