Add Fat Mach-O (Universal Binary) support

Fix fieldOffsets bug in some metadata versions
Add support for generic multi-architecture binaries
Add Mach-O section RVA mapping

Il2CppInspector/FileFormatReader.cs

@@ -5,7 +5,9 @@
 */
 
 using System;
+using System.Collections.Generic;
 using System.IO;
+using System.Runtime.CompilerServices;
 using NoisyCowStudios.Bin2Object;
 
 namespace Il2CppInspector
@@ -13,6 +15,9 @@ namespace Il2CppInspector
     public interface IFileFormatReader
     {
         BinaryObjectReader Stream { get; }
+        uint NumImages { get; }
+        IEnumerable<IFileFormatReader> Images { get; }
+        IFileFormatReader this[uint index] { get; }
         long Position { get; set; }
         string Arch { get; }
         uint GlobalOffset { get; }
@@ -35,17 +40,26 @@ namespace Il2CppInspector
 
         public BinaryObjectReader Stream => this;
 
+        public uint NumImages { get; protected set; } = 1;
+
         public uint GlobalOffset { get; protected set; }
 
         public virtual string Arch => throw new NotImplementedException();
 
-        public static T Load(string filename, uint offset = 0) {
-            using (var stream = new FileStream(filename, FileMode.Open))
-                return Load(stream, offset);
+        public IEnumerable<IFileFormatReader> Images {
+            get {
+                for (uint i = 0; i < NumImages; i++)
+                    yield return this[i];
+            }
         }
 
-        public static T Load(Stream stream, uint offset = 0) {
-            stream.Position = offset;
+        public static T Load(string filename) {
+            using (var stream = new FileStream(filename, FileMode.Open))
+                return Load(stream);
+        }
+
+        public static T Load(Stream stream) {
+            stream.Position = 0;
             var pe = (T) Activator.CreateInstance(typeof(T), stream);
             return pe.Init() ? pe : null;
         }
@@ -53,11 +67,21 @@ namespace Il2CppInspector
         // Confirm file is valid and set up RVA mappings
         protected virtual bool Init() => throw new NotImplementedException();
 
+        // Choose a sub-binary within the image for multi-architecture binaries
+        public virtual IFileFormatReader this[uint index] {
+            get {
+                if (index == 0)
+                    return this;
+                throw new IndexOutOfRangeException("Binary image index out of bounds");
+            }
+        }
+
         // Find search locations in the machine code for Il2Cpp data
         public virtual uint[] GetSearchLocations() => throw new NotImplementedException();
-        
+
         // Map an RVA to an offset into the file image
-        public virtual uint MapVATR(uint uiAddr) => throw new NotImplementedException();
+        // No mapping by default
+        public virtual uint MapVATR(uint uiAddr) => uiAddr;
 
         // Retrieve object(s) from specified RVA(s)
         public U ReadMappedObject<U>(uint uiAddr) where U : new() {