Add custom definition for win32 MSG struct

The win32 types are kinda cursed, but it makes it easy to copy&paste and check.

SDL3-CS/SDL3/ClangSharp/SDL_system.Windows.g.cs

@@ -28,10 +28,6 @@ using System.Runtime.Versioning;
 
 namespace SDL
 {
-    public partial struct tagMSG
-    {
-    }
-
     public partial struct XTaskQueueObject
     {
     }
@@ -44,7 +40,7 @@ namespace SDL
     {
         [DllImport("SDL3", CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
         [SupportedOSPlatform("Windows")]
-        public static extern void SDL_SetWindowsMessageHook([NativeTypeName("SDL_WindowsMessageHook")] delegate* unmanaged[Cdecl]<void*, tagMSG*, int> callback, void* userdata);
+        public static extern void SDL_SetWindowsMessageHook([NativeTypeName("SDL_WindowsMessageHook")] delegate* unmanaged[Cdecl]<void*, MSG*, int> callback, void* userdata);
 
         [DllImport("SDL3", CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
         [SupportedOSPlatform("Windows")]

SDL3-CS/SDL3/SDL_system.Windows.cs

@@ -0,0 +1,34 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+
+namespace SDL
+{
+    // https://learn.microsoft.com/en-us/dotnet/standard/native-interop/best-practices#common-windows-data-types
+    using LONG = int;
+    using DWORD = uint;
+    using UINT = uint;
+    using HWND = IntPtr;
+    using WPARAM = UIntPtr;
+    using LPARAM = IntPtr;
+
+    // https://learn.microsoft.com/en-us/windows/win32/api/windef/ns-windef-point
+    public struct POINT
+    {
+        public LONG x;
+        public LONG y;
+    }
+
+    // https://learn.microsoft.com/en-us/windows/win32/api/winuser/ns-winuser-msg
+    public struct MSG
+    {
+        public HWND hwnd;
+        public UINT message;
+        public WPARAM wParam;
+        public LPARAM lParam;
+        public DWORD time;
+        public POINT pt;
+        public DWORD lPrivate;
+    }
+}

SDL3-CS/SDL3/SDL_system.Windows.rsp

@@ -0,0 +1,10 @@
+# Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+# See the LICENCE file in the repository root for full licence text.
+
+# Exclude struct forward declaration
+--exclude
+tagMSG
+
+# ClangSharp recommended remapping
+--remap
+tagMSG=MSG