[Xamarin.Android.Build.Tasks] Run define constants in-process

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

@@ -10,7 +10,8 @@
 
 namespace Xamarin.Android.Tasks
 {
-	public class GetAndroidDefineConstants : AndroidTask
+	[MSBuildMultiThreadableTask]
+	public class GetAndroidDefineConstants : MultithreadedAndroidTask
 	{
 		public override string TaskPrefix => "GAD";
 

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

@@ -0,0 +1,48 @@
+#nullable enable
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.Build.Framework;
+using NUnit.Framework;
+using Xamarin.Android.Tasks;
+
+namespace Xamarin.Android.Build.Tests
+{
+	[TestFixture]
+	public class GetAndroidDefineConstantsTests
+	{
+		[TestCase ("36", null, 36, "")]
+		[TestCase ("36.1", null, 36, "__ANDROID_36_1__")]
+		[TestCase ("38.2", "11.0-rc+test", 38, "__ANDROID_36_1__;__ANDROID_37_1__;__ANDROID_37_2__;__ANDROID_37_3__;__ANDROID_37_4__;__ANDROID_38_1__;__ANDROID_38_2__")]
+		public void Constants (string apiLevel, string? productVersion, int major, string minorConstants)
+		{
+			var task = new GetAndroidDefineConstants {
+				AndroidApiLevel = apiLevel,
+				ProductVersion = productVersion,
+			};
+			Assert.IsTrue (task.Execute ());
+			var constants = task.AndroidDefineConstants ?? throw new InvalidOperationException ("No constants returned.");
+			var expected = new List<string> ();
+			if (productVersion != null)
+				expected.Add ("__XAMARIN_ANDROID_11_0_rc_test__");
+			expected.AddRange (["__MOBILE__", "__ANDROID__"]);
+			expected.AddRange (Enumerable.Range (1, major).Select (i => $"__ANDROID_{i}__"));
+			expected.AddRange (minorConstants.Split (';', StringSplitOptions.RemoveEmptyEntries));
+			CollectionAssert.AreEqual (expected, constants.Select (i => i.ItemSpec));
+		}
+
+		[TestCase ("")]
+		[TestCase ("invalid")]
+		public void InvalidApiLevel (string apiLevel)
+		{
+			var errors = new List<BuildErrorEventArgs> ();
+			var task = new GetAndroidDefineConstants {
+				AndroidApiLevel = apiLevel,
+				BuildEngine = new MockBuildEngine (TestContext.Out, errors: errors),
+			};
+			Assert.IsFalse (task.Execute ());
+			Assert.IsNull (task.AndroidDefineConstants);
+			Assert.IsEmpty (errors);
+		}
+	}
+}