src: move process object creation into node_process_object.cc

Changes `SetupProcessObject` to `CreateProessObject` which creates
the process object from scratch and return it to `Environment::Start`
to be stored in the Environment object.

PR-URL: https://github.com/nodejs/node/pull/25397


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>