Automatically load all interop assemblies before loading plugins (#777)

Assemblies are often loaded on the il2cpp side but not on the mono side, causing confusion when using reflection.
This will load all interop assemblies right before plugins are loaded, which should mostly avoid these issues at a low time cost of around 40ms.

Author: ManlyMarco

Runtimes/Unity/BepInEx.Unity.IL2CPP/IL2CPPChainloader.cs

@@ -97,6 +97,8 @@ private static IntPtr OnInvokeMethod(IntPtr method, IntPtr obj, IntPtr parameter
 
                 unhook = true;
 
+                Il2CppInteropManager.PreloadInteropAssemblies();
+
                 Instance.Execute();
             }
             catch (Exception ex)

Runtimes/Unity/BepInEx.Unity.IL2CPP/Il2CppInteropManager.cs

@@ -8,6 +8,8 @@
 using System.Security.Cryptography;
 using System.Text;
 using System.Text.RegularExpressions;
+using System.Threading;
+using System.Threading.Tasks;
 using BepInEx.Configuration;
 using BepInEx.Logging;
 using BepInEx.Unity.Common;
@@ -88,6 +90,14 @@ static Il2CppInteropManager()
          .AppendLine("{BepInEx} - Path to the BepInEx folder.")
          .AppendLine("{ProcessName} - Name of the current process")
          .ToString());
+    
+    private static readonly ConfigEntry<bool> PreloadIL2CPPInteropAssemblies = ConfigFile.CoreConfig.Bind(
+     "IL2CPP", "PreloadIL2CPPInteropAssemblies",
+     true,
+     new StringBuilder()
+         .AppendLine("Automatically load all interop assemblies right before loading plugins.")
+         .AppendLine("Some plugins may not work properly without this, but it may cause issues in some games.")
+         .ToString());
 
     private static readonly ManualLogSource Logger = BepInEx.Logging.Logger.CreateLogSource("InteropManager");
 
@@ -357,4 +367,32 @@ private static void RunIl2CppInteropGenerator(List<AssemblyDefinition> sourceAss
 
         sourceAssemblies.Do(x => x.Dispose());
     }
+
+    internal static void PreloadInteropAssemblies()
+    {
+        if (!PreloadIL2CPPInteropAssemblies.Value)
+            return;
+
+        var sw = Stopwatch.StartNew();
+
+        var files = Directory.EnumerateFiles(IL2CPPInteropAssemblyPath);
+        var loaded = 0;
+        Parallel.ForEach(files, file =>
+        {
+            if (!file.EndsWith(".dll", StringComparison.OrdinalIgnoreCase)) return;
+            if (file.Equals("netstandard.dll", StringComparison.OrdinalIgnoreCase)) return;
+            if (file.Equals("Il2Cppnetstandard.dll", StringComparison.OrdinalIgnoreCase)) return;
+            try
+            {
+                Assembly.LoadFrom(file);
+                Interlocked.Increment(ref loaded);
+            }
+            catch (Exception e)
+            {
+                Logger.LogWarning($"Failed to preload {file} - {e}");
+            }
+        });
+
+        Logger.LogDebug($"Preloaded {loaded} interop assemblies in {sw.ElapsedMilliseconds}ms");
+    }
 }