[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 ();
+ }
  }
 -->
  <classabstract="false"deprecated="not deprecated"extends="xamarin.test.PackageClass"extends-generic-aware="xamarin.test.PackageClass"final="false"name="PublicClass"static="false"visibility="public">
  <constructordeprecated="not deprecated"final="false"name="PublicClass"static="false"visibility="public" />
  <methodabstract="false"deprecated="not deprecated"final="false"name="foo"native="false"return="void"static="false"synchronized="false"visibility="public">
  </method>
  </class>
+ <interfaceabstract="true"deprecated="not deprecated"final="false"name="PublicClass.OnPressedChangeListener"static="true"visibility="" >
+ <methodabstract="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=newList<GenBase>();
+varnested_removes=newList<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(vargeningens){
+foreach(varnestingen.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(varnestinnested_removes)
+gen.NestedTypes.Remove(nest);
+
+nested_removes.Clear();
+}
+
 foreach(GenBasegeninremoved)
 gens.Remove(gen);
 }while(removed.Count>0);