[Xamarin.Android.Tools.Bytecode] @not-null androidx.annotation.NonNull (#759)

Context: 18c29b7
Context: https://developer.android.com/reference/androidx/annotation/NonNull

Set `//*/@not-null` and/or `//*/@return-not-null` to `true` when
encountering the `androidx.annotation.NonNull` annotation.

Author: jpobst

src/Xamarin.Android.Tools.Bytecode/XmlClassDeclarationBuilder.cs

@@ -464,6 +464,7 @@ static bool IsNotNullAnnotation (Annotation annotation)
 			// https://stackoverflow.com/questions/4963300/which-notnull-java-annotation-should-i-use
 			switch (annotation.Type) {
 				case "Landroid/annotation/NonNull;":
+				case "Landroidx/annotation/NonNull;":
 				case "Landroidx/annotation/RecentlyNonNull;":
 				case "Ljavax/validation/constraints/NotNull;":
 				case "Ledu/umd/cs/findbugs/annotations/NonNull;":