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/TrapException.cs

@@ -0,0 +1,41 @@
+using System;
+using System.Runtime.InteropServices;
+using System.Runtime.Serialization;
+
+namespace Wasmtime
+{
+    /// <summary>
+    /// The exception for WebAssembly traps.
+    /// </summary>
+    [Serializable]
+    public class TrapException : WasmtimeException
+    {
+        /// <inheritdoc/>
+        public TrapException() { }
+
+        /// <inheritdoc/>
+        public TrapException(string message) : base(message) { }
+
+        /// <inheritdoc/>
+        public TrapException(string message, Exception inner) : base(message, inner) { }
+
+        /// <inheritdoc/>
+        protected TrapException(SerializationInfo info, StreamingContext context) : base(info, context) { }
+
+        internal static TrapException FromOwnedTrap(IntPtr trap)
+        {
+            unsafe
+            {
+                Interop.wasm_trap_message(trap, out var bytes);
+                var message = Marshal.PtrToStringUTF8((IntPtr)bytes.data, (int)bytes.size - 1 /* remove null */);
+                Interop.wasm_byte_vec_delete(ref bytes);
+
+                Interop.wasm_trap_delete(trap);
+
+                return new TrapException(message);
+            }
+        }
+
+        // TODO: expose trap frames
+    }
+}