[msbuild] Fix building apps with extensions remotely.

Pending: the actual fix.

For now this only has a test.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/2542958.

Author: rolfbjarne

tests/dotnet/UnitTests/ProjectTest.cs

@@ -1868,6 +1868,19 @@ public void KillEverything ()
 		[TestCase (ApplePlatform.MacOSX, "osx-x64;osx-arm64", true)]
 		// [TestCase ("MacCatalyst", "")] - No extension support yet
 		public void BuildProjectsWithExtensions (ApplePlatform platform, string runtimeIdentifier, bool isNativeAot)
+		{
+			BuildProjectsWithExtensionsImpl (platform, runtimeIdentifier, isNativeAot);
+		}
+
+		[TestCase (ApplePlatform.iOS, "ios-arm64", false)]
+		[Category ("RemoteWindows")]
+		public void BuildProjectsWithExtensionsOnRemoteWindows (ApplePlatform platform, string runtimeIdentifier, bool isNativeAot)
+		{
+			Configuration.IgnoreIfNotOnWindows ();
+			BuildProjectsWithExtensionsImpl (platform, runtimeIdentifier, isNativeAot, AddRemoteProperties ());
+		}
+
+		void BuildProjectsWithExtensionsImpl (ApplePlatform platform, string runtimeIdentifier, bool isNativeAot, Dictionary<string, string>? properties = null)
 		{
 			Configuration.IgnoreIfIgnoredPlatform (platform);
 			var consumingProjectDir = GetProjectPath ("ExtensionConsumer", runtimeIdentifier, platform, out var appPath);
@@ -1876,7 +1889,7 @@ public void BuildProjectsWithExtensions (ApplePlatform platform, string runtimeI
 			Clean (extensionProjectDir);
 			Clean (consumingProjectDir);
 
-			var properties = GetDefaultProperties (runtimeIdentifier);
+			properties = GetDefaultProperties (runtimeIdentifier, extraProperties: properties);
 
 			if (isNativeAot) {
 				properties ["PublishAot"] = "true";