Fixed the generated C# when a function uses an external specialisation.

Signed-off-by: Dimitar Dobrev <dpldobrev@protonmail.com>

src/Generator/Passes/TrimSpecializationsPass.cs

@@ -97,8 +97,15 @@ namespace CppSharp.Passes
         private void CleanSpecializations(Class template)
         {
             template.Specializations.RemoveAll(s =>
-                s.SpecializationKind == TemplateSpecializationKind.Undeclared ||
-                (!specializations.Contains(s) && !internalSpecializations.Contains(s)));
+                {
+                    if (s.SpecializationKind == TemplateSpecializationKind.Undeclared ||
+                        (!specializations.Contains(s) && !internalSpecializations.Contains(s)))
+                    {
+                        s.ExplicitlyIgnore();
+                        return true;
+                    }
+                    return false;
+                });
 
             foreach (var specialization in template.Specializations.Where(
                 s => s is ClassTemplatePartialSpecialization))

tests/NamespacesDerived/NamespacesDerived.cpp

@@ -70,6 +70,11 @@ DerivedFromExternalSpecialization::~DerivedFromExternalSpecialization()
 {
 }
 
+TemplateWithIndependentFields<Base3> DerivedFromExternalSpecialization::returnExternalSpecialization()
+{
+    return TemplateWithIndependentFields<Base3>();
+}
+
 HasVirtualInDependency::HasVirtualInDependency()
 {
 }

tests/NamespacesDerived/NamespacesDerived.h

@@ -76,6 +76,7 @@ class DLL_API DerivedFromExternalSpecialization : public TemplateWithIndependent
 public:
     DerivedFromExternalSpecialization();
     ~DerivedFromExternalSpecialization();
+    TemplateWithIndependentFields<Base3> returnExternalSpecialization();
 };
 
 class DLL_API DerivedFromSecondaryBaseInDependency : public Derived, public SecondaryBase