Added a UITest

Author: kubaflo

src/Controls/tests/TestCases.HostApp/Issues/Issue12156.xaml

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+<?xml version="1.0" encoding="utf-8" ?>
+<Shell xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+       xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+       xmlns:ios="clr-namespace:Microsoft.Maui.Controls.PlatformConfiguration.iOSSpecific;assembly=Microsoft.Maui.Controls"
+       ios:Page.LargeTitleDisplay="Always"
+       x:Class="Maui.Controls.Sample.Issues.Issue12156">
+
+    <ShellContent Title="Home">
+        <ContentPage>
+            <Label
+                Text="Issue 12156"
+                AutomationId="Label"
+                VerticalOptions="Center"
+                HorizontalOptions="Center"/>
+        </ContentPage>
+    </ShellContent>
+
+</Shell>

src/Controls/tests/TestCases.HostApp/Issues/Issue12156.xaml.cs

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+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 12156, "iOS Page.LargeTitleDisplay does not work on iOS", PlatformAffected.iOS)]
+public partial class Issue12156 : Shell
+{
+	public Issue12156()
+	{
+		InitializeComponent();
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue12156.cs

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+#if TEST_FAILS_ON_ANDROID && TEST_FAILS_ON_ANDROID && TEST_FAILS_ON_WINDOWS
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue12156 : _IssuesUITest
+{
+	public Issue12156(TestDevice testDevice) : base(testDevice)
+	{
+	}
+
+	public override string Issue => "iOS Page.LargeTitleDisplay does not work on iOS";
+
+	[Test]
+	[Category(UITestCategories.TitleView)]
+	public void LargeTitleDisplayWorks()
+	{
+		App.WaitForElement("Label");
+		VerifyScreenshot();
+	}
+}
+#endif