Bring managed iOS client to feature parity

clients/apple/dotnet/VoiceCat.iOS/IosScreenCapture.cs

@@ -0,0 +1,23 @@
+using System.Runtime.InteropServices;
+using Foundation;
+
+namespace VoiceCat.iOS;
+
+internal static partial class IosScreenCapture
+{
+    internal static void Present()
+    {
+        if (!OperatingSystem.IsIOSVersionAtLeast(27)) return;
+        NSUrl? root = NSFileManager.DefaultManager.GetContainerUrl(IosConstants.AppGroup);
+        if (root?.Path is null) throw new InvalidOperationException("The VoiceCat App Group is unavailable.");
+        string path = Path.Combine(root.Path, "voicecat", "broadcast_audio.ring"); Directory.CreateDirectory(Path.GetDirectoryName(path)!);
+        if (Available() == 0) throw new InvalidOperationException("Screen audio sharing is unavailable on this device."); PresentNative(path);
+    }
+
+    [LibraryImport("__Internal", EntryPoint = "vc_ios_screen_capture_available")]
+    private static partial int Available();
+    [LibraryImport("__Internal", EntryPoint = "vc_ios_screen_capture_present", StringMarshalling = StringMarshalling.Utf8)]
+    private static partial void PresentNative(string ringPath);
+    [LibraryImport("__Internal", EntryPoint = "vc_ios_screen_capture_stop")]
+    internal static partial void Stop();
+}