Fixes #4534 - Use content_loaded instead of io.element.join for detecting EC timeouts. Bump EC to 0.16.0-rc.4.

ElementX/Sources/Screens/CallScreen/CallScreenModels.swift

@@ -106,7 +106,7 @@ enum CallScreenJavaScriptMessageName: String, CaseIterable {
 
 struct DecodedWidgetMessage: Decodable {
     private static let decoder = JSONDecoder()
-    private static let joinAction = "io.element.join"
+    private static let contentLoadedAction = "content_loaded"
     private static let fromWidget = "fromWidget"
     
     let action: String?
@@ -119,7 +119,7 @@ struct DecodedWidgetMessage: Decodable {
         return try decoder.decode(DecodedWidgetMessage.self, from: data)
     }
     
-    var hasJoined: Bool {
-        action == Self.joinAction && api == Self.fromWidget
+    var hasLoaded: Bool {
+        action == Self.contentLoadedAction && api == Self.fromWidget
     }
 }