Move Wasmtime for .NET to the Wasmtime repo.

This moves the Wasmtime for .NET implementation to the Wasmtime repo.

Wasmtime for .NET is a binding of the Wasmtime API for use in .NET.

crates/misc/dotnet/tests/Fixtures/ModuleFixture.cs

@@ -0,0 +1,43 @@
+using System;
+using System.IO;
+using Wasmtime;
+
+namespace Wasmtime.Tests
+{
+    public abstract class ModuleFixture : IDisposable
+    {
+        public ModuleFixture()
+        {
+            Engine = new Engine();
+            Store = Engine.CreateStore();
+            Module = Store.CreateModule(Path.Combine("Modules", ModuleFileName));
+        }
+
+        public void Dispose()
+        {
+            if (Module != null)
+            {
+                Module.Dispose();
+                Module = null;
+            }
+
+            if (Store != null)
+            {
+                Store.Dispose();
+                Store = null;
+            }
+
+            if (Engine != null)
+            {
+                Engine.Dispose();
+                Engine = null;
+            }
+        }
+
+        public Engine Engine { get; set; }
+        public Store Store { get; set; }
+        public Module Module { get; set; }
+
+        protected abstract string ModuleFileName { get; }
+    }
+}