[Testing] Added UI Test for manual test D12 (#18677)

* Added UI Test

* Added snapshots

* Updated snapshot

src/Controls/samples/Controls.Sample.UITests/Issues/Issue18675.xaml

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+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.Issue18675">
+    <ScrollView>
+        <VerticalStackLayout>
+            <Label 
+                AutomationId="WaitForStubControl"
+                Text="1. The test fails if the placeholder text in the editor below is missing." />
+            <Editor 
+                AutomationId="IsReadOnlyEditor"
+                IsReadOnly="True"
+                Placeholder="testing" />
+            <Label 
+                Text="2. The test fails if the placeholder text in the editor below is not blue." />
+            <Editor 
+                IsReadOnly="True"
+                Placeholder="testing"
+                PlaceholderColor="Blue" />
+        </VerticalStackLayout>
+    </ScrollView>
+</ContentPage>

src/Controls/samples/Controls.Sample.UITests/Issues/Issue18675.xaml.cs

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+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Xaml;
+
+namespace Maui.Controls.Sample.Issues
+{
+	[XamlCompilation(XamlCompilationOptions.Compile)]
+	[Issue(IssueTracker.ManualTest, "D12", "Editor IsReadOnly property prevent from modifying the text", PlatformAffected.All)]
+	public partial class Issue18675 : ContentPage
+	{
+		public Issue18675()
+		{
+			InitializeComponent();
+		}
+	}
+}

src/Controls/tests/UITests/Tests/Issues/Issue18675.cs

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+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.AppiumTests.Issues
+{
+	public class Issue186751 : _IssuesUITest
+	{
+		public Issue186751(TestDevice device) : base(device)
+		{
+		}
+
+		public override string Issue => "Editor IsReadOnly property prevent from modifying the text";
+
+		[Test]
+		public void EditorIsReadOnlyPreventModify()
+		{
+			App.WaitForElement("WaitForStubControl");
+
+			// 1.The test fails if the placeholder text in the editor below is missing.
+			App.Click("IsReadOnlyEditor");
+
+			// 2. The test fails if the placeholder text in the editor below is not blue.
+			VerifyScreenshot();
+		}
+	}
+}