Add DoubleBackground state (#3710)

Task/Issue URL: https://app.asana.com/0/0/1208930420896743/f

**Description**:
Add DoubleBackground state to discover what events are called after we
end up in this weird state.

DuckDuckGo/AppLifecycle/AppStateTransitions.swift

@@ -90,17 +90,48 @@ extension Background {
             return Active(application: application)
         case .openURL:
             return self
-        case .launching, .suspending, .backgrounding:
+        case .backgrounding:
+            return DoubleBackground()
+        case .launching, .suspending:
             return handleUnexpectedEvent(event)
         }
     }
 
 }
 
+extension DoubleBackground {
+
+    func apply(event: AppEvent) -> any AppState {
+        // report event so we know what events can be called at this moment, but do not let SM be stuck in this state just not to be flooded with these events
+        _ = handleUnexpectedEvent(event)
+
+        switch event {
+        case .activating(let application):
+            return Active(application: application)
+        case .suspending(let application):
+            return Inactive(application: application)
+        case .launching, .backgrounding, .openURL:
+            return self
+        }
+
+    }
+
+}
+
 extension InactiveBackground {
 
     func apply(event: AppEvent) -> any AppState {
-        handleUnexpectedEvent(event)
+        // report event so we know what events can be called at this moment, but do not let SM be stuck in this state just not to be flooded with these events
+        _ = handleUnexpectedEvent(event)
+
+        switch event {
+        case .activating(let application):
+            return Active(application: application)
+        case .suspending(let application):
+            return Inactive(application: application)
+        case .launching, .backgrounding, .openURL:
+            return self
+        }
     }
 
 }

DuckDuckGo/AppLifecycle/AppStates/Background.swift

@@ -26,3 +26,7 @@ struct Background: AppState {
     }
 
 }
+
+struct DoubleBackground: AppState {
+
+}