[lib/native] introduce useUpdateSystemTheme

Summary:
Now that we want to bring updateThemeInfo redux actions/state into web as well there are several things we should lift from native into lib so that we can share them across both platforms. This diff lifts the common logic in ThemeHandler into a hook that can be consumed by each respective platform's ThemeHandler

Part of https://linear.app/comm/issue/ENG-4956/lift-any-necessary-shared-types-selectors-functions-for-storing-the

Depends on D9550

Test Plan: flow and confirmed that the logic in updateSystemTheme still works as expected

Reviewers: atul, inka, rohan

Reviewed By: atul

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9551