[lib] Introduce new SET_DATA_LOADED action

Summary:
This is the first part of ENG-4048.

Context: dataLoaded is used in isLoggedIn here, which is in turn used in LogInHandler here to decide when to dismiss LoggedOutModal and the other accountModals (such as RegistrationNavigator).

We want to defer dismissal until the avatar setting keyserver endpoint returns. The easiest way to do that is make sure dataLoaded doesn't get set at the end of register. To achieve that, I'm going to use a separate Redux action to set dataLoaded, and in a later diff will stop registration from setting dataLoaded.

Test Plan: Tested registration (SIWE and otherwise) flows on native and web

Reviewers: atul, ginsu

Reviewed By: atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8107