Fix warn for mismatch on > MonoAndroid90

Newer versions of android shouldn't warn when using android support since there is never going to be an android support for those newer api levels.

Author: Redth

source/buildtasks/support-annotations/NugetPackages.cs

@@ -16,17 +16,14 @@ namespace Xamarin.Android.Support.BuildTasks
 {
 	public static class NugetPackages
 	{
-		public static readonly Dictionary<int, Version> AndroidApiLevelsAndVersions = new Dictionary<int, Version>
+		static readonly Dictionary<int, Version> AndroidApiLevelsAndVersions = new Dictionary<int, Version>
 		{
 			{ 23, new Version(6, 0) },
 			{ 24, new Version(7, 0) },
 			{ 25, new Version(7, 1) },
 			{ 26, new Version(8, 0) },
 			{ 27, new Version(8, 1) },
-			{ 28, new Version(9, 0) },
-			{ 28, new Version(9, 1) },
-			{ 28, new Version(10, 0) },
-			{ 28, new Version(10, 1) },
+			{ 28, new Version(9, 0) }
 		};
 
 		public static int GetMajorVersion(string version)

source/buildtasks/support-annotations/VerifyVersionsTask.cs

@@ -104,11 +104,19 @@ public override bool Execute()
 			{
 				var supportVersion = packageVersions[pkgId];
 
+                // Eg: if we have support 27.x installed, we'd get the recommended framework back of 8.1
 				var frameworkForSupportVersion = NugetPackages.FrameworkVersionForSupportVersion(supportVersion);
 				var apiLevelForSupportVersion = NugetPackages.GetMajorVersion(supportVersion);
 
+                // Eg: if (8.1 < our project's target framework version)
 				if (frameworkForSupportVersion < frameworkVersion)
-					invalidSupportVersionsForFramework.Add(Tuple.Create(pkgId, supportVersion, apiLevelForSupportVersion, frameworkForSupportVersion));
+                {
+                    // We only want to add this warning if the target framework is <= MonoAndroid90 since after that
+                    // there are no more support libraries to match the android api level, instead users should move to androidx
+                    // we may in the future add a warning here to upgrade to androidx in these cases
+                    if (frameworkVersion <= new Version(9, 0))
+                        invalidSupportVersionsForFramework.Add(Tuple.Create(pkgId, supportVersion, apiLevelForSupportVersion, frameworkForSupportVersion));
+                }	
 			}
 
 			if (invalidSupportVersionsForFramework.Any())