Do not use underscores in the ApplicationId

Underscores are not supported on Windows

src/TestUtils/src/Microsoft.Maui.IntegrationTests/TemplateTests.cs

@@ -1,3 +1,4 @@
+using System.Xml.Linq;
 using Microsoft.Maui.IntegrationTests.Apple;
 
 namespace Microsoft.Maui.IntegrationTests
@@ -47,6 +48,33 @@ public void Build(string id, string framework, string config, bool shouldPack)
 				$"Project {Path.GetFileName(projectFile)} failed to build. Check test output/attachments for errors.");
 		}
 
+		[Test]
+		// with spaces
+		[TestCase("maui", "Project Space", "projectspace")]
+		[TestCase("maui-blazor", "Project Space", "projectspace")]
+		[TestCase("mauilib", "Project Space", "projectspace")]
+  		// with invalid characters
+		[TestCase("maui", "Project@Symbol", "projectsymbol")]
+		[TestCase("maui-blazor", "Project@Symbol", "projectsymbol")]
+		[TestCase("mauilib", "Project@Symbol", "projectsymbol")]
+		public void BuildsWithSpecialCharacters(string id, string projectName, string expectedId)
+		{
+			var projectDir = TestDirectory;
+			var projectFile = Path.Combine(projectDir, $"{projectName}.csproj");
+
+			Assert.IsTrue(DotnetInternal.New(id, projectDir, DotNetCurrent),
+				$"Unable to create template {id}. Check test output for errors.");
+
+			EnableTizen(projectFile);
+
+ 			var doc = XDocument.Load(docPath);
+			var appId = doc.Root.Elements("PropertyGroup").Element("ApplicationId").Value;
+			Assert.AreEqual($"com.companyname.{expectedId}", appId);
+
+			Assert.IsTrue(DotnetInternal.Build(projectFile, "Debug", properties: BuildProps, msbuildWarningsAsErrors: true),
+				$"Project {Path.GetFileName(projectFile)} failed to build. Check test output/attachments for errors.");
+		}
+
 		[Test]
 		// Parameters: short name, target framework, build config, use pack target
 		[TestCase("maui", DotNetPrevious, "Debug", false)]