[generator] Do bind package-private nested types (#575)

Fixes: #572

Do not bind ["package private"][0] nested types   For example, given:

	public class OuterExample {
	    /* package */ static class InnerExample {
	    }
	}

The type `OuterExample.InnerExample` *should not be bound*.

Previously `OuterExample.InnerExample` *would* be bound as a
*`public`* type (?!), which could result in later Java Callable Wrapper
compilation errors, if/when they attempted to access the
package-private types

This change causes package-private nested types to behave the same as
top-level package-private types, which were never bound.

[0]: https://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html

Author: jpobst

tests/generator-Tests/expected/AccessModifiers/AccessModifiers.xml

@@ -18,13 +18,21 @@
 			public class PublicClass extends PackageClass {
 				@Override
 				public void foo();
+				
+				// This nested type should not be generated because it is package-private
+				/* package */ static interface OnPressedChangeListener {
+				  void onPressedChanged ();
+				}
 			}
 		-->
 		<class abstract="false" deprecated="not deprecated" extends="xamarin.test.PackageClass" extends-generic-aware="xamarin.test.PackageClass" final="false" name="PublicClass" static="false" visibility="public">
 			<constructor deprecated="not deprecated" final="false" name="PublicClass" static="false" visibility="public" />
 			<method abstract="false" deprecated="not deprecated" final="false" name="foo" native="false" return="void" static="false" synchronized="false" visibility="public">
 			</method>
 		</class>
+		<interface abstract="true" deprecated="not deprecated" final="false" name="PublicClass.OnPressedChangeListener" static="true" visibility="" >
+			<method abstract="true" deprecated="not deprecated" final="false" name="onPressedChanged" jni-signature="V" bridge="false" native="false" return="void" jni-return="V" static="false" synchronized="false" synthetic="false" visibility="public" />
+		</interface>
 		<!-- 
 			/* package */ abstract class ExtendPackageClass extends PackageClass {
 			}

tools/generator/CodeGenerator.cs

@@ -232,6 +232,8 @@ static void Validate (List<GenBase> gens, CodeGenerationOptions opt, CodeGenerat
 		{
 			//int cycle = 1;
 			List<GenBase> removed = new List<GenBase> ();
+			var nested_removes = new List<GenBase> ();
+
 			// This loop is required because we cannot really split type validation and member
 			// validation apart (unlike C# compiler), because invalidated members will result
 			// in the entire interface invalidation (since we cannot implement it), and use of
@@ -254,6 +256,22 @@ static void Validate (List<GenBase> gens, CodeGenerationOptions opt, CodeGenerat
 						removed.Add (gen);
 					}
 
+				// Remove any nested types that are package-private
+				foreach (var gen in gens) {
+					foreach (var nest in gen.NestedTypes)
+						if (opt.IgnoreNonPublicType && (nest.RawVisibility != "public" && nest.RawVisibility != "internal")) {
+							// We still add it to "removed" even though the removal
+							// code later won't work, so that it triggers a new cycle
+							removed.Add (nest);
+							nested_removes.Add (nest);
+						}
+
+					foreach (var nest in nested_removes)
+						gen.NestedTypes.Remove (nest);
+
+					nested_removes.Clear ();
+				}
+
 				foreach (GenBase gen in removed)
 					gens.Remove (gen);
 			} while (removed.Count > 0);