Initial implementation of AccountSettings. (#6275)

* Make the UserPreference macro also generate an accessor for the key name.

* Initial implementation of AccountSettings.

- Add an AccountUserDefaults storage with a userID prefix on the key.
- Migrate the 2 values reset by AppSettings.resetSessionSpecificSettings to AccountSettings.

* Rename UserSettings.volatile() to UserSettings.mock()

Given it now has a userID parameter with a default value..

ElementX/Sources/Screens/PinnedEventsTimelineScreen/View/PinnedEventsTimelineScreen.swift

@@ -83,7 +83,7 @@ struct PinnedEventsTimelineScreen: View {
 struct PinnedEventsTimelineScreen_Previews: PreviewProvider, TestablePreview {
     static let viewModel = PinnedEventsTimelineScreenViewModel(roomProxy: JoinedRoomProxyMock(.init()),
                                                                userIndicatorController: UserIndicatorControllerMock(),
-                                                               userSettings: .volatile(),
+                                                               userSettings: .mock(),
                                                                analyticsService: AnalyticsServiceMock(.init()))
     
     static let emptyTimelineViewModel = makeTimelineViewModel(timelineItems: [])
@@ -106,7 +106,7 @@ struct PinnedEventsTimelineScreen_Previews: PreviewProvider, TestablePreview {
         let eventIDs = timelineItems.compactMap { ($0 as? EventBasedTimelineItemProtocol)?.id.eventID }
         let timelineController = TimelineControllerMock(.init(timelineKind: .pinned, timelineItems: timelineItems))
         
-        let userSettings = UserSettings.volatile()
+        let userSettings = UserSettings.mock()
         userSettings.messageMultiSelectEnabled = isSelecting
         let userSession = UserSessionMock(.init(userSettings: userSettings))
         
@@ -117,7 +117,7 @@ struct PinnedEventsTimelineScreen_Previews: PreviewProvider, TestablePreview {
                                                   userIndicatorController: UserIndicatorControllerMock(),
                                                   appMediator: AppMediatorMock(.init()),
                                                   analyticsService: AnalyticsServiceMock(.init()),
-                                                  emojiProvider: EmojiProvider(userSettings: .volatile()),
+                                                  emojiProvider: EmojiProvider(userSettings: .mock()),
                                                   linkMetadataProvider: LinkMetadataProvider(),
                                                   timelineControllerFactory: TimelineControllerFactoryMock(.init()))