Improve type resolution for unstripping (#158)

* Support PinnedTypeSignature
* Support CustomModifierTypeSignature
* Resolve nested types with the correct priority
* Handle BoxedTypeSignature and FunctionPointerTypeSignature

SentinelTypeSignature

Function pointers and boxed types

Il2CppInterop.Generator/Passes/Pass80UnstripMethods.cs

@@ -187,7 +187,7 @@ private static PropertyDefinition GetOrCreateProperty(MethodDefinition unityMeth
         if (unityType is ByReferenceTypeSignature)
         {
             var resolvedElementType = ResolveTypeInNewAssemblies(context, unityType.GetElementType(), imports);
-            return resolvedElementType == null ? null : new ByReferenceTypeSignature(resolvedElementType);
+            return resolvedElementType?.MakeByReferenceType();
         }
 
         if (unityType is ArrayBaseTypeSignature arrayType)
@@ -203,20 +203,25 @@ private static PropertyDefinition GetOrCreateProperty(MethodDefinition unityMeth
             return new GenericInstanceTypeSignature(genericBase.ToTypeDefOrRef(), false, resolvedElementType);
         }
 
-        if (unityType.DeclaringType != null)
+        if (unityType is PointerTypeSignature)
         {
-            var enclosingResolvedType = ResolveTypeInNewAssembliesRaw(context, unityType.DeclaringType.ToTypeSignature(), imports);
-            if (enclosingResolvedType == null) return null;
-            var resolvedNestedType = enclosingResolvedType.Resolve()!.NestedTypes
-                .FirstOrDefault(it => it.Name == unityType.Name);
-
-            return resolvedNestedType?.ToTypeSignature();
+            var resolvedElementType = ResolveTypeInNewAssemblies(context, unityType.GetElementType(), imports);
+            return resolvedElementType?.MakePointerType();
         }
 
-        if (unityType is PointerTypeSignature)
+        if (unityType is PinnedTypeSignature)
         {
             var resolvedElementType = ResolveTypeInNewAssemblies(context, unityType.GetElementType(), imports);
-            return resolvedElementType?.MakePointerType();
+            return resolvedElementType?.MakePinnedType();
+        }
+
+        if (unityType is CustomModifierTypeSignature customModifier)
+        {
+            var resolvedElementType = ResolveTypeInNewAssemblies(context, customModifier.BaseType, imports);
+            var resolvedModifierType = ResolveTypeInNewAssemblies(context, customModifier.ModifierType.ToTypeSignature(), imports);
+            return resolvedElementType is not null && resolvedModifierType is not null
+                ? new CustomModifierTypeSignature(resolvedModifierType.ToTypeDefOrRef(), customModifier.IsRequired, resolvedElementType)
+                : null;
         }
 
         if (unityType is GenericInstanceTypeSignature genericInstance)
@@ -234,6 +239,25 @@ private static PropertyDefinition GetOrCreateProperty(MethodDefinition unityMeth
             return newInstance;
         }
 
+        if (unityType is BoxedTypeSignature)
+            return null; // Boxed types are not yet supported
+
+        if (unityType is FunctionPointerTypeSignature)
+            return null; // Function pointers are not yet supported
+
+        if (unityType is SentinelTypeSignature)
+            return unityType; // SentinelTypeSignature has no state and be reused.
+
+        if (unityType.DeclaringType != null)
+        {
+            var enclosingResolvedType = ResolveTypeInNewAssembliesRaw(context, unityType.DeclaringType.ToTypeSignature(), imports);
+            if (enclosingResolvedType == null) return null;
+            var resolvedNestedType = enclosingResolvedType.Resolve()!.NestedTypes
+                .FirstOrDefault(it => it.Name == unityType.Name);
+
+            return resolvedNestedType?.ToTypeSignature();
+        }
+
         var targetAssemblyName = unityType.Scope!.Name!;
         if (targetAssemblyName.EndsWith(".dll"))
             targetAssemblyName = targetAssemblyName.Substring(0, targetAssemblyName.Length - 4);