[web] Update threadActivityStore[activeThread].lastNavigatedTo state

Summary:
While the motivations for introducing threadActivityStore were about improving performance on native, we're making parallel changes to web for consistency.

Depends on D9402

Test Plan:
Navigated to various threads and checked threadActivityStore updated as expected (this is safe to land, will introduce migrations that clean things up when ripping out lastNavigatedTo and lastPruned from messageStore.threads):

Reviewers: ashoat, tomek, ginsu

Reviewed By: ashoat

Subscribers: wyilio

Differential Revision: https://phab.comm.dev/D9404