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/ImportAttribute.cs

@@ -0,0 +1,31 @@
+using System;
+
+namespace Wasmtime
+{
+    /// <summary>
+    /// Used to mark .NET methods and fields as imports to a WebAssembly module.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Field)]
+    public class ImportAttribute : Attribute
+    {
+        /// <summary>
+        /// Constructs a new <see cref="ImportAttribute"/>.
+        /// </summary>
+        /// <param name="name">The name of the import.</param>
+        public ImportAttribute(string name)
+        {
+            Name = name;
+        }
+
+        /// <summary>
+        /// The name of the import.
+        /// </summary>
+        public string Name { get; set; }
+
+        /// <summary>
+        /// The module name of the import.
+        /// </summary>
+        /// <remarks>A null or empty module name implies that the import is not scoped to a module.</remarks>
+        public string Module { get; set; }
+    }
+}