Generate Threshold{Class,Type} properties for all classes

If a class derives from `Java.Lang.Object` it should have the two properties
mentioned above generated, so that it is possible to find methods in the correct
instance of Java class instance that is wrapped by our managed class.

Generator used to decide whether or not to generate these properties based on
the presence of class members (fields, constructors, methods and properties) or
whether the class is an annotation in the API description file.

However there exist a number of classes (for instance `Inet4Address`) which don't
have any of the members present and yet they should have the Threshold*
properties generated for the reasons described above.

The `HasClassHandle` property which was used to determine whether the class should
get these properties (among a handful of other members) doesn't serve its
purpose correctly leading to corner cases when the `Threshold*` properties are
missing and causing runtime bugs (e.g. calling `GetAddress()` on an instance of
`Inet4Address` returns `null` even though the underlying Java class has the
information - the call never reaches `Inet4Address` instance and thus returns
nothing).

Replacing `HasClassHandle` with a simple check for whether the class in question
derives from `Java.Lang.Object` is the correct fix that ensures the missing
properties are generated.

Fixe https://bugzilla.xamarin.com/show_bug.cgi?id=56537

Author: grendello

tools/generator/ClassGen.cs

@@ -160,10 +160,6 @@ public override string NativeType {
 			get { return "IntPtr"; }
 		}
 
-		public bool HasClassHandle {
-			get { return ctors.Count > 0 || Fields.Count > 0 || Methods.Count > 0 || Properties.Count > 0 || IsAnnotation; }
-		}
-
 		public IList<Ctor> Ctors {
 			get { return ctors; }
 		}
@@ -449,17 +445,16 @@ public override void Generate (StreamWriter sw, string indent, CodeGenerationOpt
 				sw.WriteLine ();
 			}
 
-			if (HasClassHandle) {
-				bool requireNew = false;
+			bool requireNew = InheritsObject;
+			if (!requireNew) {
 				for (var bg = BaseGen; bg != null && bg is XmlClassGen; bg = bg.BaseGen) {
-					if (bg.HasClassHandle) {
+					if (bg.InheritsObject) {
 						requireNew = true;
 						break;
 					}
 				}
-
-				opt.CodeGenerator.WriteClassHandle (this, sw, indent, opt, requireNew);
 			}
+			opt.CodeGenerator.WriteClassHandle (this, sw, indent, opt, requireNew);
 
 			GenConstructors (sw, indent + "\t", opt);