Address review: fix Windows Rect ambiguity, add iOS frame guard

- Use fully qualified Microsoft.Maui.Graphics.Rect in ShellTests to fix
  Windows compilation error (CS0246)
- Add 'if (Shell.Frame != destination)' guard in iOS ShellRenderer to
  avoid unnecessary frame updates during layout passes
- Remove unused 'using Microsoft.Maui.Graphics' import
- Restore original whitespace formatting in using directives

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: kubaflo

src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellRenderer.cs

@@ -142,7 +142,9 @@ public override void ViewDidLayoutSubviews()
 			if (_currentShellItemRenderer != null)
 				_currentShellItemRenderer.ViewController.View.Frame = View.Bounds;
 
-			Shell.Frame = View.Bounds.ToRectangle();
+			var destination = View.Bounds.ToRectangle();
+			if (Shell.Frame != destination)
+				Shell.Frame = destination;
 		}
 
 		public override void ViewDidLoad()

src/Controls/tests/DeviceTests/Elements/Shell/ShellTests.cs

@@ -12,15 +12,14 @@
 using Microsoft.Maui.Controls.Handlers.Items;
 using Microsoft.Maui.Devices;
 using Microsoft.Maui.DeviceTests.Stubs;
-using Microsoft.Maui.Graphics;
 using Microsoft.Maui.Handlers;
 using Microsoft.Maui.Hosting;
 using Microsoft.Maui.Platform;
 using Xunit;
 using static Microsoft.Maui.DeviceTests.AssertHelpers;
+
 #if ANDROID || IOS || MACCATALYST
 using ShellHandler = Microsoft.Maui.Controls.Handlers.Compatibility.ShellRenderer;
-
 #endif
 
 #if IOS || MACCATALYST
@@ -1158,7 +1157,7 @@ public async Task SettingFrameDoesTriggerInvalidatedMeasure()
 				measureInvalidatedCount++;
 			};
 
-			shell.Frame = new Rect(0, 0, 100, 100);
+			shell.Frame = new Microsoft.Maui.Graphics.Rect(0, 0, 100, 100);
 
 			await CreateHandlerAndAddToWindow<IWindowHandler>(shell, _ =>
 			{