Add support for base (proxy) class (#29)

tests/ProxyInterfaceSourceGeneratorTests/Source/Human.cs

@@ -1,7 +1,11 @@
+using Xunit.Sdk;
+
 namespace ProxyInterfaceSourceGeneratorTests.Source
 {
     public class Human
     {
         public bool IsAlive { get; set; }
+
+        public string GetterOnly => "x";
     }
 }

tests/ProxyInterfaceSourceGeneratorTests/Source/IMyStruct.cs

@@ -0,0 +1,6 @@
+namespace ProxyInterfaceSourceGeneratorTests.Source
+{
+    public partial interface IMyStruct
+    {
+    }
+}

tests/ProxyInterfaceSourceGeneratorTests/Source/MyStruct.cs

@@ -0,0 +1,7 @@
+namespace ProxyInterfaceSourceGeneratorTests.Source
+{
+    public struct MyStruct
+    {
+        public int Id { get; set; }
+    }
+}

tests/ProxyInterfaceSourceGeneratorTests/Source/Person.cs

@@ -1,9 +1,15 @@
+using System.Collections.Generic;
 using System.Threading.Tasks;
 
 namespace ProxyInterfaceSourceGeneratorTests.Source
 {
-    public class Person
+    public class Person : Human
     {
+        public IList<Human> AddHuman(Human h)
+        {
+            return new List<Human> { h, new Human { IsAlive = true } };
+        }
+
         public string Name { get; set; }
 
         public string? StringNullable { get; set; }

tests/ProxyInterfaceSourceGeneratorTests/Source/PersonExtends.cs

@@ -1,3 +1,4 @@
+using System.Collections.Generic;
 using System.Threading.Tasks;
 
 namespace ProxyInterfaceSourceGeneratorTests.Source