Tests: Add new test assemblies for C# features (#36)

* Add new test assemblies for C# features

Three of these test assemblies go over several important features of C#,
organized by C# language version. PartialGenericTypes stresses closed
and partially closed generics. Finally, VTablesAndLayout tests the
layout of classes when translated to C++, and also contains code which
calls vtable and interface functions to test reverse engineering.

* Tests: Update .csproj

* Tests: Update .csproj

Co-authored-by: Katy Coe <djkaty@users.noreply.github.com>

Il2CppTests/TestSources/CSharp1.cs

@@ -0,0 +1,57 @@
+using System;
+
+/* C# 1.0 feature test */
+namespace Il2CppTests.TestSources
+{
+    public class SimpleClass : SimpleInterface
+    {
+        public SimpleStruct ss;
+        public int i;
+
+        public static SimpleStruct StaticFunc(SimpleStruct ss) {
+            Console.WriteLine(ss);
+            return new SimpleStruct();
+        }
+
+        public SimpleStruct InstanceFunc(SimpleStruct ss) {
+            Console.WriteLine(ss);
+            return this.ss;
+        }
+
+        public int func(int val) {
+            return val + 42;
+        }
+
+        public delegate SimpleStruct SimpleDelegate(SimpleStruct ss);
+        public event SimpleDelegate SimpleEvent;
+        public int SimpleProperty {
+            get { return 0; }
+            set { SimpleEvent(ss); }
+        }
+    }
+
+    public struct SimpleStruct : SimpleInterface
+    {
+        public SimpleClass sc;
+        public int i;
+
+        public static SimpleStruct StaticFunc(SimpleStruct ss) {
+            Console.WriteLine(ss);
+            return new SimpleStruct();
+        }
+
+        public SimpleClass InstanceFunc(SimpleStruct ss) {
+            Console.WriteLine(ss);
+            return this.sc;
+        }
+
+        public int func(int val) {
+            return ((SimpleInterface)sc).func(val) + 13;
+        }
+    }
+
+    public interface SimpleInterface
+    {
+        int func(int val);
+    }
+}