[lib/native/web] factor out remaining shared logic + copy for thread notification settings

Summary:
This diff factors out more logic + copy that will be shared in the thread notifications settings across web and native

Depends on D12654

Test Plan: Confirmed that there were no regressions with the thread notications settings on web

Reviewers: ashoat, inka

Reviewed By: inka

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12661