[Xamarin.Android.Build.Tests] Prevent build logs locking up IDEs (#1876)

When running tests in Visual Studio's test runner UI (Windows and
macOS), a test failure causes an unpleasant experience:

Since the entire MSBuild diagnostic log is contained within a
`FailedBuildException`, the UI will hang anywhere from 30 seconds to
1 minute while it tries to render the exception details in the IDE.

The solution here is to:

  - Detect if the unit test is running inside an IDE
  - Don't include the build log in the exception details in this case

On Windows, we can detect the test running by the process name, which
is either `testhost.x86` or `testhost.x64`.

On macOS, we can detect VS for Mac by looking for the
`MONO_GAC_PREFIX` environment variable, which points to
`/Applications/Visual Studio.app/Contents/Resources` by default.

If neither of these cases are met, such as command line, the exception
remains unchanged.

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/Builder.cs

@@ -393,12 +393,36 @@ protected bool BuildInternal (string projectOrSolution, string target, string []
 			}
 			if (!result && ThrowOnBuildFailure) {
 				string message = "Build failure: " + Path.GetFileName (projectOrSolution) + (BuildLogFile != null && File.Exists (buildLogFullPath) ? "Build log recorded at " + buildLogFullPath : null);
-				throw new FailedBuildException (message, null, File.ReadAllText (buildLogFullPath));
+				//NOTE: enormous logs will lock up IDE's UI
+				if (IsRunningInIDE) {
+					throw new FailedBuildException (message);
+				} else {
+					throw new FailedBuildException (message, null, File.ReadAllText (buildLogFullPath));
+				}
 			}
 
 			return result;
 		}
 
+		bool IsRunningInIDE {
+			get {
+				//Check for Windows, process is testhost.x86 in VS 2017
+				using (var p = Process.GetCurrentProcess ()) {
+					if (p.ProcessName.IndexOf ("testhost", StringComparison.OrdinalIgnoreCase) != -1) {
+						return true;
+					}
+				}
+
+				//Check for macOS, value is normally /Applications/Visual Studio.app/Contents/Resources
+				var gac_prefix = Environment.GetEnvironmentVariable ("MONO_GAC_PREFIX", EnvironmentVariableTarget.Process);
+				if (!string.IsNullOrEmpty (gac_prefix) && gac_prefix.IndexOf ("Visual Studio", StringComparison.OrdinalIgnoreCase) != -1) {
+					return true;
+				}
+
+				return false;
+			}
+		}
+
 		string QuoteFileName (string fileName)
 		{
 			return fileName.Contains (" ") ? $"\"{fileName}\"" : fileName;