[tests] Be more flexible when parsing build-tools versions (#4354)

Context: https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=3520928&view=ms.vss-test-web.build-test-results-tab&runId=11613622&resultId=100500&paneView=debug

The **Xamarin.Android.Build.Tests - macOS** job has started reporting
some failures within the past couple of days:

	System.FormatException : Input string was not in a correct format.
	    at System.Number.ThrowOverflowOrFormatException (System.Boolean overflow, System.String overflowResourceKey)
	    at System.Number.ParseInt32 (System.ReadOnlySpan`1[T] value, System.Globalization.NumberStyles styles, System.Globalization.NumberFormatInfo info)
	    at System.Int32.Parse (System.ReadOnlySpan`1[T] s, System.Globalization.NumberStyles style, System.IFormatProvider provider)
	    at System.Version.TryParseComponent (System.ReadOnlySpan`1[T] component, System.String componentName, System.Boolean throwOnFailure, System.Int32& parsedComponent)
	    at System.Version.ParseVersion (System.ReadOnlySpan`1[T] input, System.Boolean throwOnFailure)
	    at System.Version.Parse (System.String input)
	    at System.Version..ctor (System.String version)
	    at Xamarin.Android.Build.Tests.BaseTest+<>c.<GetPathToLatestBuildTools>b__48_0 (System.String x)
	    at System.Linq.EnumerableSorter`2[TElement,TKey].ComputeKeys (TElement[] elements, System.Int32 count)
	    at System.Linq.EnumerableSorter`1[TElement].ComputeMap (TElement[] elements, System.Int32 count)
	    at System.Linq.EnumerableSorter`1[TElement].Sort (TElement[] elements, System.Int32 count)
	    at System.Linq.OrderedEnumerable`1[TElement].SortedMap (System.Linq.Buffer`1[TElement] buffer)
	    at System.Linq.OrderedEnumerable`1+<GetEnumerator>d__3[TElement].MoveNext ()
	    at Xamarin.Android.Build.Tests.BaseTest.GetPathToLatestBuildTools (System.String exe)
	    at Xamarin.Android.Build.Tests.BaseTest.GetPathToAapt ()
	    at Xamarin.Android.Build.Tests.ManagedResourceParserTests.CompareAaptAndManagedParserOutputWithCustomIds ()

What's happened is that somehow, for some reason,
Build-tools 30.0.0-rc1 has been installed onto the build machine:

	$HOME/Library/Android/sdk/build-tools/30.0.0-rc1

`30.0.0-rc` cannot be parsed by `System.Version`.

I think we can be a bit more lenient when locating the latest version
of build-tools by instead using a string comparison.  This will also
allow the relevant tests to use a preview version of build-tools if
they exist.

Additional logging has also been added to confirm this hypothesis,
which is how we determined that it's Build-tools 30.0.0-rc1.

Author: pjcollins

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Utilities/BaseTest.cs

@@ -407,7 +407,8 @@ protected byte [] ReadAllBytesIgnoringLineEndings (Stream stream)
 		protected string GetPathToLatestBuildTools (string exe)
 		{
 			var path = Path.Combine (AndroidSdkPath, "build-tools");
-			foreach (var dir in Directory.GetDirectories (path, "*", SearchOption.TopDirectoryOnly).OrderByDescending (x => new Version (Path.GetFileName (x)))) {
+			foreach (var dir in Directory.GetDirectories (path, "*", SearchOption.TopDirectoryOnly).OrderByDescending (x => Path.GetFileName (x))) {
+				TestContext.Out.WriteLine ($"Found build tools version: {dir}.");
 				var aapt2 = Path.Combine (dir, exe);
 				if (File.Exists (aapt2))
 					return dir;