Remove some redundant injections when passed alongside a user session too.
# Conflicts:
# ElementX/Sources/Screens/PinnedEventsTimelineScreen/View/PinnedEventsTimelineScreen.swift
# ElementX/Sources/Screens/Timeline/TimelineViewModel.swift
* Add an AccountProvider type and use it within AppSettings.
* Use the AccountProvider type within the Authentication flow too.
* Fix unit test compilation with Swift 6.4
* Make sure defaultAccountProvider takes allowOtherAccountProviders into account.
* Document a caveat on using AuthenticationService.homeserver.value.accountProvider.