Display an icon in the room header for rooms with shared history (#5016)

* feat: Display an icon in the room header for rooms with shared history

* fix: Apply suggestions from code review

- Simplifies `isRoomHistoryShared` expressions using type inferrence.
- Adds failure messages to unit test.

Co-authored-by: Doug <6060466+pixlwave@users.noreply.github.com>

* fix: Remove extension method in favour of field on configuration.

* fix: Distinguish between `shared` and `worldReadable` icons.

* refactor: Use `RoomHistorySharingState` enum with extension methods

---------

Co-authored-by: Doug <6060466+pixlwave@users.noreply.github.com>

ElementX/Sources/Mocks/JoinedRoomProxyMock.swift

@@ -27,6 +27,7 @@ struct JoinedRoomProxyMockConfiguration {
     var canonicalAlias: String?
     var alternativeAliases: [String] = []
     var pinnedEventIDs: Set<String> = []
+    var historyVisibility: RoomHistoryVisibility = .shared
     
     var timelineStartReached = false
     
@@ -190,7 +191,7 @@ extension RoomInfoProxyMock {
         unreadMentionsCount = 0
         pinnedEventIDs = configuration.pinnedEventIDs
         joinRule = configuration.joinRule
-        historyVisibility = .shared
+        historyVisibility = configuration.historyVisibility
         
         powerLevels = RoomPowerLevelsProxyMock(configuration: configuration.powerLevelsConfiguration)
     }