Rename some methods in RuntimeScheduler_Modern to refer to event loop more explicitly (#45143)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/45143

Changelog: [internal]

Just a small refactor of some private methods in `RuntimeScheduler_Modern` to refer to some concepts in terms of the event loop.

Reviewed By: christophpurrer

Differential Revision: D58948811

fbshipit-source-id: 979c78ccd4cf5d96f00061049366171934b43ee2