lib: move process prototype manipulation into setupProcessObject

Since no operation is requiring process to be an EventEmitter before
setupProcessObject is called, it's safe to set up the prototype chain
in setupProcessObject and make the main code path more readable.

PR-URL: https://github.com/nodejs/node/pull/24089


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>