Extract and start to split theme.

Riot/ModulesSwiftUI/Common/ViewFrameReader/ViewFrameReader.swift

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+// 
+// 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 Foundation
+import SwiftUI
+
+/**
+ Used to calculate the frame of a view. Useful in situations as with `ZStack` where
+ you might want to layout views using alignment guides.
+ Example usage:
+ ```
+ @State private var frame: CGRect = CGRect.zero
+ ...
+ SomeView()
+    .background(ViewFrameReader(frame: $frame))
+ 
+ ```
+ */
+@available(iOS 14.0, *)
+struct ViewFrameReader: View {
+    @Binding var frame: CGRect
+    
+    var body: some View {
+        GeometryReader { geo -> Color in
+            DispatchQueue.main.async {
+                frame = geo.frame(in: .local)
+            }
+            return .clear
+        }
+    }
+}