Listen to call decline to stop ringing when declined from other device (#4505)

* Listen to call decline to stop ringing when declined from other device

* use proper swift naming convention for Id/ID

* fix Force unwrapping

* fix lint

* An approach without the custom publisher.

* review: correct naming convention

* review: revert some invisible char/tab changes

* add ref to the room proxy in the closure

---------

Co-authored-by: Doug <douglase@element.io>

ElementX/Sources/Services/Room/JoinedRoomProxy.swift

@@ -649,6 +649,17 @@ class JoinedRoomProxy: JoinedRoomProxyProtocol {
         }
     }
     
+    /// Subscribe to call decline events from that rtc notification event.
+    func subscribeToCallDeclineEvents(rtcNotificationEventID: String, listener: CallDeclineListener) -> Result<TaskHandle, RoomProxyError> {
+        do {
+            let handle = try room.subscribeToCallDeclineEvents(rtcNotificationEventId: rtcNotificationEventID, listener: listener)
+            return .success(handle)
+        } catch {
+            MXLog.error("Failed observing rtc decline with error: \(error)")
+            return .failure(.sdkError(error))
+        }
+    }
+    
     // MARK: - Permalinks
     
     func matrixToPermalink() async -> Result<URL, RoomProxyError> {