src: name all builtin init functions Initialize

This commit renames a few of the builtin modules init functions to
Initialize for consistency.

PR-URL: https://github.com/nodejs/node/pull/19550


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>