src: move handle properties to prototype

Reduce the size of wrap objects by moving a couple of accessors from the
instance template to the prototype template.  They occupied one slot per
instance instead of one slot per class.

This commit fixes some instances of unwrapping twice since that code had
to be updated anyway to use `args.This()` instead of `args.Holder()`.

PR-URL: https://github.com/nodejs/node/pull/16482


Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>