Instrument missing screen metrics (#5764)

* Instrument missing screen metrics

- Done

RiotSwiftUI/Modules/Common/Util/ScreenTrackerViewModifier.swift

@@ -0,0 +1,40 @@
+// 
+// Copyright 2021 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import SwiftUI
+
+@available(iOS 14.0, *)
+/// `ScreenTrackerViewModifier` is a helper class used to track PostHog screen from SwiftUI screens.
+struct ScreenTrackerViewModifier: ViewModifier {
+    let screen: AnalyticsScreen
+    
+    @ViewBuilder
+    func body(content: Content) -> some View {
+        content
+            .onAppear {
+                #if canImport(MatrixSDK)
+                Analytics.shared.trackScreen(screen)
+                #endif
+            }
+    }
+}
+
+@available(iOS 14.0, *)
+extension View {
+    func track(screen: AnalyticsScreen) -> some View {
+        return self.modifier(ScreenTrackerViewModifier(screen: screen))
+    }
+}