[xabt] Fix @(AndroidLibrary) with %(Pack)=false (#10365)

Fixes: #8504

The `<CreateAar/>` MSBuild task was not respecting the `%(Pack)=false`
metadata on `@(AndroidLibrary)` items, causing jar files to be
included in AAR packages even when explicitly marked for exclusion.

This caused issues for developers who wanted to:

- Reference binding projects without packaging the underlying jar
  files
- Create modular architectures where jars are packaged separately
- Avoid duplicate jar inclusion in complex dependency scenarios

## Solution

Modified the jar processing loop in `CreateAar.cs` to:

- Check the `Pack` metadata on each jar file item
- Skip jars with `Pack='false'` using `continue;`
- Add debug logging for transparency when jars are skipped
- Preserve default behavior (include jars when Pack is unspecified or
  'true')

## Testing

Added comprehensive test `AndroidLibraryPackFalseExcludesJarFromAar`
that:

- Creates a binding project with both `Pack='false'` and default Pack
  jars  
- Verifies the AAR is generated successfully
- Examines actual AAR contents to confirm Pack='false' jars are
  excluded
- Confirms default behavior jars are still included

Co-authored-by: Jonathan Peppers <[email protected]>

Author: Copilot

src/Xamarin.Android.Build.Tasks/Tasks/CreateAar.cs

@@ -100,6 +100,11 @@ public override bool RunTask ()
 				}
 				if (JarFiles != null) {
 					foreach (var jar in JarFiles) {
+						var pack = jar.GetMetadata ("Pack");
+						if (string.Equals (pack, "false", StringComparison.OrdinalIgnoreCase)) {
+							Log.LogDebugMessage ($"Skipping jar '{jar.ItemSpec}' because Pack='false'");
+							continue;
+						}
 						var archivePath = $"libs/{GetHashedFileName (jar)}.jar";
 						aar.AddStream (File.OpenRead (jar.ItemSpec), archivePath);
 						existingEntries.Remove (archivePath);

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/BindingBuildTest.cs

@@ -9,6 +9,7 @@
 using Xamarin.ProjectTools;
 using Microsoft.Android.Build.Tasks;
 using Microsoft.Build.Framework;
+using Xamarin.Tools.Zip;
 
 namespace Xamarin.Android.Build.Tests
 {
@@ -437,6 +438,43 @@ public void OnUpdate (Java.Lang.Object p0)
 			}
 		}
 
+		[Test]
+		public void AndroidLibraryPackFalseExcludesJarFromAar ()
+		{
+			var binding = new XamarinAndroidBindingProject () {
+				IsRelease = true,
+			};
+			// Add a jar with Pack='false' - should not be included in AAR
+			binding.OtherBuildItems.Add (new AndroidItem.AndroidLibrary ("Jars\\test-pack-false.jar") {
+				BinaryContent = () => ResourceData.JavaSourceJarTestJar,
+				MetadataValues = "Pack=false;Bind=false",
+			});
+			// Add a jar with Pack='true' (default) - should be included in AAR
+			binding.OtherBuildItems.Add (new AndroidItem.AndroidLibrary ("Jars\\test-pack-true.jar") {
+				BinaryContent = () => ResourceData.JavaSourceJarTestJar,
+				MetadataValues = "Bind=false",
+			});
+
+			using (var bindingBuilder = CreateDllBuilder ()) {
+				Assert.IsTrue (bindingBuilder.Build (binding), "binding build should have succeeded");
+
+				// Check that the AAR file was created
+				var aarPath = Path.Combine (Root, bindingBuilder.ProjectDirectory, binding.OutputPath, "UnnamedProject.aar");
+				FileAssert.Exists (aarPath);
+
+				// Extract and examine AAR contents
+				using (var aar = ZipArchive.Open (aarPath, FileMode.Open)) {
+					// test-pack-false.jar should NOT be in the AAR because Pack='false'
+					var packFalseEntry = aar.Where (e => e.FullName.Contains ("test-pack-false")).FirstOrDefault ();
+					Assert.IsNull (packFalseEntry, "Jar with Pack='false' should not be included in AAR");
+
+					// test-pack-true.jar should be in the AAR (default Pack='true')
+					var packTrueEntry = aar.Where (e => e.FullName.Contains ("test-pack-true") || e.FullName.StartsWith ("libs/")).FirstOrDefault ();
+					Assert.IsNotNull (packTrueEntry, "Jar with Pack='true' (default) should be included in AAR");
+				}
+			}
+		}
+
 		[Test]
 		public void RemoveEventHandlerResolution ()
 		{