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/src/Engine.cs

@@ -0,0 +1,44 @@
+using System;
+
+namespace Wasmtime
+{
+    /// <summary>
+    /// Represents the Wasmtime engine.
+    /// </summary>
+    public class Engine : IDisposable
+    {
+        /// <summary>
+        /// Constructs a new <see cref="Engine" />.
+        /// </summary>
+        public Engine()
+        {
+            Handle = Interop.wasm_engine_new();
+
+            if (Handle.IsInvalid)
+            {
+                throw new WasmtimeException("Failed to create Wasmtime engine.");
+            }
+        }
+
+        /// <summary>
+        /// Creates a new Wasmtime <see cref="Store" />.
+        /// </summary>
+        /// <returns>Returns the new <see cref="Store" />.</returns>
+        public Store CreateStore()
+        {
+            return new Store(this);
+        }
+
+        /// <inheritdoc/>
+        public void Dispose()
+        {
+            if (!Handle.IsInvalid)
+            {
+                Handle.Dispose();
+                Handle.SetHandleAsInvalid();
+            }
+        }
+
+        internal Interop.EngineHandle Handle { get; private set; }
+    }
+}