Add in-app screenshot preventing (#606)

In-app screenshot preventing fixes

client/platforms/ios/ScreenProtection.swift

@@ -0,0 +1,87 @@
+import UIKit
+
+public func toggleScreenshots(_ isEnabled: Bool) {
+  let window = UIApplication.shared.keyWindows.first!
+
+  if isEnabled {
+    ScreenProtection.shared.disable(for: window.rootViewController!.view)
+  } else {
+    ScreenProtection.shared.enable(for: window.rootViewController!.view)
+  }
+}
+
+extension UIApplication {
+  var keyWindows: [UIWindow] {
+    connectedScenes
+      .compactMap {
+        if #available(iOS 15.0, *) {
+          ($0 as? UIWindowScene)?.keyWindow
+        } else {
+          ($0 as? UIWindowScene)?.windows.first { $0.isKeyWindow }
+        }
+      }
+  }
+}
+
+class ScreenProtection {
+  public static let shared = ScreenProtection()
+
+  var pairs = [ProtectionPair]()
+
+  private var blurView: UIVisualEffectView?
+  private var recordingObservation: NSKeyValueObservation?
+
+  public func enable(for view: UIView) {
+    DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) {
+      view.subviews.forEach {
+        self.pairs.append(ProtectionPair(from: $0))
+      }
+    }
+  }
+
+  public func disable(for view: UIView) {
+    DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) {
+      self.pairs.forEach {
+        $0.removeProtection()
+      }
+
+      self.pairs.removeAll()
+    }
+  }
+}
+
+struct ProtectionPair {
+  let textField: UITextField
+  let layer: CALayer
+
+  init(from view: UIView) {
+    let secureTextField = UITextField()
+    secureTextField.backgroundColor = .clear
+    secureTextField.translatesAutoresizingMaskIntoConstraints = false
+    secureTextField.isSecureTextEntry = true
+
+    view.insertSubview(secureTextField, at: 0)
+    secureTextField.isUserInteractionEnabled = false
+
+    view.layer.superlayer?.addSublayer(secureTextField.layer)
+    secureTextField.layer.sublayers?.last?.addSublayer(view.layer)
+
+    secureTextField.topAnchor.constraint(equalTo: view.topAnchor, constant: 0).isActive = true
+    secureTextField.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: 0).isActive = true
+    secureTextField.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0).isActive = true
+    secureTextField.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0).isActive = true
+
+    self.init(textField: secureTextField, layer: view.layer)
+  }
+
+  init(textField: UITextField, layer: CALayer) {
+    self.textField = textField
+    self.layer = layer
+  }
+
+  func removeProtection() {
+    textField.superview?.superview?.layer.addSublayer(layer)
+    textField.layer.removeFromSuperlayer()
+    textField.removeFromSuperview()
+  }
+}