Finish extraction

- Moves SwiftUI code out of Riot and into RiotSwiftUI which has no dependency on Matrix SDK.
- Git wasn't smart enough to see the file moves. Most feature function has remain unchanged. 1 change I did make was remove NotificationSettingsViewModel's dependence on MxPushRule, so that the view model could be moved into RiotSwiftUI.
- Add LocaleProvider to abstract VectorL10n's use of Matrix SDK language so it can be used in RiotSwiftUI.
- Split Theme into UKit/SwiftUI version to remove RiotSwiftUI's dependence on ThemeService and ThemeV1.
- Migrated from ThemeObserver to ThemePublisher. We push updates to ThemePublisher so that we can remove ThemeService as dependency.
- Add .DS_Store to .gitignore

RiotSwiftUI/Modules/Common/ActivityIndicator/ActivityIndicator.swift

@@ -0,0 +1,49 @@
+// 
+// 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
+
+/**
+ A visual cue to user that something is in progress.
+ */
+@available(iOS 14.0, *)
+struct ActivityIndicator: View {
+    
+    private enum Constants {
+        static let backgroundColor = Color(UIColor(white: 0.8, alpha: 0.9))
+    }
+    
+    var body: some View {
+        ProgressView()
+            .progressViewStyle(CircularProgressViewStyle(tint: Color.white))
+            .padding()
+            .background(Constants.backgroundColor)
+            .cornerRadius(5)
+            
+    }
+}
+
+@available(iOS 14.0, *)
+struct ActivityIndicator_Previews: PreviewProvider {
+    static var previews: some View {
+        Group {
+            Text("Hello World!")
+                .activityIndicator(show: true)
+            Text("Hello World!")
+                .activityIndicator(show: false)
+        }
+    }
+}