Add default string invoker shim.

src/Platforms/Echo.Platforms.AsmResolver/Emulation/Invocation/DefaultInvokers.cs

@@ -42,6 +42,11 @@ public static class DefaultInvokers
         /// Gets the method invoker that steps over any method by invoking it via System.Reflection. 
         /// </summary>
         public static ReflectionInvoker ReflectionInvoke => ReflectionInvoker.Instance;
+
+        /// <summary>
+        /// Gets the default shim for the <see cref="System.String"/> type.
+        /// </summary>
+        public static StringInvoker StringShim => StringInvoker.Instance;
 
         /// <summary>
         /// Gets the method invoker that forwards any method that is not within the resolution scope of the current

src/Platforms/Echo.Platforms.AsmResolver/Emulation/Invocation/StringInvoker.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Collections.Generic;
+using AsmResolver.DotNet;
+using Echo.Memory;
+using Echo.Platforms.AsmResolver.Emulation.Dispatch;
+
+namespace Echo.Platforms.AsmResolver.Emulation.Invocation;
+
+/// <summary>
+/// Implements a method invoker that shims methods from the <see cref="System.String"/> class.
+/// </summary>
+public class StringInvoker : IMethodInvoker
+{
+    /// <summary>
+    /// Gets the singleton instance of the <see cref="StringInvoker"/> class.
+    /// </summary>
+    public static StringInvoker Instance { get; } = new();
+
+    /// <inheritdoc />
+    public InvocationResult Invoke(CilExecutionContext context, IMethodDescriptor method, IList<BitVector> arguments)
+    {
+        if ((!method.DeclaringType?.IsTypeOf("System", "String") ?? true) || method.Signature is null)
+            return InvocationResult.Inconclusive();
+
+        switch (method.Name?.Value)
+        {
+            case "FastAllocateString":
+                return InvokeFastAllocateString(context, arguments);
+
+            default:
+                return InvocationResult.Inconclusive();
+        }
+    }
+
+    private static InvocationResult InvokeFastAllocateString(CilExecutionContext context, IList<BitVector> arguments)
+    {
+        var length = arguments[0];
+        if (!length.IsFullyKnown)
+            throw new CilEmulatorException("Cannot allocate a string with an unknown length.");
+
+        long address = context.Machine.Heap.AllocateString(length.AsSpan().I32, true);
+        var result = context.Machine.ValueFactory.RentNativeInteger(address);
+
+        return InvocationResult.StepOver(result);
+    }
+}