[SDK] Introduce winbase_undoc.h for undocumented exported kernel32 definitions (#8019)

This header is based on the following files from the official
Windows 10.0.10240.0 PSDK, a copy of which can be found at:
- https://github.com/tpn/winsdk-10/blob/master/Include/10.0.10240.0/um/minwin/winbasep.h
- https://github.com/tpn/winsdk-10/blob/master/Include/10.0.10240.0/um/minwin/wbasek.h

CODEOWNERS

···
 #   M:
 #   R: HBelusca, Hermès Bélusca-Maïto
 #   S: Maintained
+/sdk/include/reactos/winbase_undoc.h        @HBelusca
+/subsystems/win/basesrv/
 /win32ss/user/winsrv/
 /win32ss/user/winsrv/usersrv/harderror.c    @HBelusca
 

base/services/schedsvc/job.c

···
 /* INCLUDES *****************************************************************/
 
 #include "precomp.h"
+#include <winbase_undoc.h>
 
 WINE_DEFAULT_DEBUG_CHANNEL(schedsvc);
 

base/services/schedsvc/precomp.h

···
 #include <winreg.h>
 #include <winsvc.h>
 #include <winuser.h>
-#include <undocuser.h>
 
 #include <ndk/rtlfuncs.h>
 

base/system/services/database.c

···
 
 #include "services.h"
 
+#include <winbase_undoc.h>
 #include <userenv.h>
 #include <strsafe.h>
-
-#include <reactos/undocuser.h>
 
 #define NDEBUG
 #include <debug.h>

base/system/winlogon/screensaver.c

···
 /* INCLUDES *****************************************************************/
 
 #include "winlogon.h"
+#include <winbase_undoc.h>
 
 /* FUNCTIONS ****************************************************************/
 

base/system/winlogon/winlogon.h

···
 /* PSEH for SEH Support */
 #include <pseh/pseh2.h>
 
-#include <reactos/undocuser.h>
-#include <reactos/undocmpr.h>
+#include <undocuser.h>
+#include <undocmpr.h>
 
 BOOL
 WINAPI

dll/win32/kernel32/include/kernel32.h

···
 #define __EXCEPT_PAGE_FAULT _SEH2_EXCEPT(_SEH2_GetExceptionCode() == STATUS_ACCESS_VIOLATION)
 #define __ENDTRY _SEH2_END
 
-/* Undocumented CreateProcess flag */
-#define STARTF_SHELLPRIVATE         0x400
-
 typedef struct _CODEPAGE_ENTRY
 {
     LIST_ENTRY Entry;

dll/win32/kernel32/k32.h

···
 #define WIN32_NO_STATUS
 #include <windef.h>
 #include <winbase.h>
+#include <winbase_undoc.h>
 #include <wingdi.h>
 #include <winreg.h>
 #include <wincon.h>

dll/win32/shell32/shelldesktop/shelldesktop.h

···
 #include <atlcom.h>
 #include <atlwin.h>
 #include <undocshell.h>
-#include <undocuser.h>
 
 #include <shellutils.h>
 #include "CChangeNotifyServer.h"

dll/win32/shell32/shellmenu/shellmenu.h

···
 #include <atlcom.h>
 #include <atlwin.h>
 #include <undocshell.h>
-#include <undocuser.h>
 
 #include <shellutils.h>
 #include <ui/rosctrls.h>

dll/win32/shell32/shlexec.cpp

···
  */
 
 #include "precomp.h"
+#include <winbase_undoc.h>
 #include <undocshell.h>
 
 WINE_DEFAULT_DEBUG_CHANNEL(exec);
 
 EXTERN_C BOOL PathIsExeW(LPCWSTR lpszPath);
 
-#ifndef STARTF_SHELLPRIVATE
-#define STARTF_SHELLPRIVATE 0x400 // From kernel32.h
-#endif
 #define SEE_MASK_CLASSALL (SEE_MASK_CLASSNAME | SEE_MASK_CLASSKEY)
 
 typedef UINT_PTR (*SHELL_ExecuteW32)(const WCHAR *lpCmd, WCHAR *env, BOOL shWait,

sdk/include/psdk/winbase.h

···
 #define STARTF_TITLEISAPPID     0x00001000
 #define STARTF_PREVENTPINNING   0x00002000
 #endif /* (WINVER >= 0x400) */
+#if (WINVER >= 0x0600)
+#define STARTF_UNTRUSTEDSOURCE  0x00008000
+#endif /* (WINVER >= 0x0600) */
 
 #define TC_NORMAL 0
 #define TC_HARDERR 1

sdk/include/reactos/undocuser.h

···
 #ifndef _UNDOCUSER_H
 #define _UNDOCUSER_H
 
+#pragma once
+
 #ifdef __cplusplus
 extern "C" {
 #endif /* defined(__cplusplus) */
···
 #define DFCS_MENUARROWDOWN 0x0010
 
 //
-// Undocumented flags for CreateProcess
+// Win32-user-specific undocumented flags for CreateProcess
 //
+#ifndef STARTF_INHERITDESKTOP
 #define STARTF_INHERITDESKTOP   0x40000000
 #define STARTF_SCREENSAVER      0x80000000
+#endif
+
 
 #define MOD_WINLOGON_SAS 0x8000
 
···
 } /* extern "C" */
 #endif /* defined(__cplusplus) */
 
-#endif
+#endif /* _UNDOCUSER_H */

sdk/include/reactos/winbase_undoc.h

···
+/*
+ * PROJECT:     ReactOS SDK
+ * LICENSE:     Dual-licensed:
+ *              LGPL-2.1-or-later (https://spdx.org/licenses/LGPL-2.1-or-later)
+ *              MIT (https://spdx.org/licenses/MIT)
+ * PURPOSE:     Undocumented Base API definitions, absent from winbase.h
+ * COPYRIGHT:   Copyright 2025 Hermès Bélusca-Maïto <[e-mail]>
+ *
+ * REMARK: This header is based on the following files from the official
+ * Windows 10.0.10240.0 PSDK, a copy of which can be found at:
+ * - https://github.com/tpn/winsdk-10/blob/master/Include/10.0.10240.0/um/minwin/winbasep.h
+ * - https://github.com/tpn/winsdk-10/blob/master/Include/10.0.10240.0/um/minwin/wbasek.h
+ */
+
+#ifndef _WINBASE_UNDOC_H
+#define _WINBASE_UNDOC_H
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * Undocumented flags for CreateProcess
+ */
+#if (WINVER >= 0x400)
+#define STARTF_HASSHELLDATA     0x00000400 // As seen in um/minwin/winbasep.h
+#define STARTF_SHELLPRIVATE     STARTF_HASSHELLDATA // ReactOS-specific name
+#endif /* (WINVER >= 0x400) */
+#if (WINVER >= 0x0A00)
+#define STARTF_TITLEISLOCALALLOCED  0x00004000
+#endif /* (WINVER >= 0x0A00) */
+#define STARTF_INHERITDESKTOP   0x40000000
+#define STARTF_SCREENSAVER      0x80000000
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _WINBASE_UNDOC_H */

win32ss/pch.h

···
 typedef struct _SECURITY_ATTRIBUTES SECURITY_ATTRIBUTES, *LPSECURITY_ATTRIBUTES;
 #define MAKEINTATOM(i) (LPWSTR)((ULONG_PTR)((WORD)(i)))
 #define WINBASEAPI
-#define STARTF_USESHOWWINDOW 1
-#define STARTF_USESIZE 2
-#define STARTF_USEPOSITION 4
+#define STARTF_USESHOWWINDOW    0x00000001
+#define STARTF_USESIZE          0x00000002
+#define STARTF_USEPOSITION      0x00000004
+#define STARTF_USEHOTKEY        0x00000200
 #include <windef.h>
 
 // Needed because windef.h messes up CDECL for whatever

win32ss/user/ntuser/main.c

···
 
 #include <win32k.h>
 #include <napi.h>
+#include <winbase_undoc.h>
 
 #define NDEBUG
 #include <debug.h>
 #include <kdros.h>
-
-#ifndef STARTF_USEHOTKEY
-#define STARTF_USEHOTKEY    0x0200
-#endif
-#ifndef STARTF_SHELLPRIVATE
-#define STARTF_SHELLPRIVATE 0x0400
-#endif
 
 HANDLE hModuleWin;