Added a UiTest (#18832)

src/Controls/samples/Controls.Sample.UITests/Issues/Issue18832.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.Issue18832"
+             xmlns:ns="clr-namespace:Maui.Controls.Sample.Issues">
+    <VerticalStackLayout>
+        <Label Text="Button: "/>
+        <Button AutomationId="button" Text="Hello, World!" CharacterSpacing="10" FontSize="30"/>
+        <Label Text="Label: "/>
+        <Label AutomationId="label" Text="Hello, World!" CharacterSpacing="10" FontSize="30"/>
+    </VerticalStackLayout>
+</ContentPage>

src/Controls/samples/Controls.Sample.UITests/Issues/Issue18832.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.Github, 18832, "[iOS] Button CharacterSpacing makes FontSize fixed and large", PlatformAffected.iOS)]
+	public partial class Issue18832 : ContentPage
+	{
+		public Issue18832()
+		{
+			InitializeComponent();
+		}
+	}
+}

src/Controls/tests/UITests/Tests/Issues/Issue18832.cs

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+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.AppiumTests.Issues
+{
+	public class Issue18832 : _IssuesUITest
+	{
+		public override string Issue => "[iOS] Button CharacterSpacing makes FontSize fixed and large";
+
+		public Issue18832(TestDevice device) : base(device)
+		{
+		}
+
+		[Test]
+		public void SizesOfBothTextsShouldHaveTheSameAndCharacterSpacing()
+		{
+			this.IgnoreIfPlatforms(new TestDevice[] { TestDevice.Android, TestDevice.Mac, TestDevice.Windows });
+
+			_ = App.WaitForElement("button");
+
+			// The test passes if both "Hello, World!" texts are of the same size
+			// and have the same character spacing
+			VerifyScreenshot();
+		}
+	}
+}