[SHELL32][SDK] Implement IsSuspendAllowed (#5831)

- Add IsShutdownAllowed helper function.
- Add IsSuspendAllowed prototype to
  <undocshell.h>.
- Implement IsSuspendAllowed function.

dll/win32/shell32/stubs.cpp

@@ -783,17 +783,6 @@ DAD_DragEnterEx2(HWND hwndTarget,
     return FALSE;
 }
 
-/*
- * Unimplemented
- */
-EXTERN_C BOOL
-WINAPI
-IsSuspendAllowed(VOID)
-{
-    FIXME("IsSuspendAllowed() stub\n");
-    return FALSE;
-}
-
 /*
  * Unimplemented
  */

dll/win32/shell32/utils.cpp

@@ -164,6 +164,20 @@ Quit:
     return ret;
 }
 
+BOOL IsShutdownAllowed(VOID)
+{
+    return SHTestTokenPrivilegeW(NULL, SE_SHUTDOWN_NAME);
+}
+
+/*************************************************************************
+ *                IsSuspendAllowed (SHELL32.53)
+ */
+BOOL WINAPI IsSuspendAllowed(VOID)
+{
+    TRACE("()\n");
+    return IsShutdownAllowed() && IsPwrSuspendAllowed();
+}
+
 /*************************************************************************
  *                SHGetShellStyleHInstance (SHELL32.749)
  */

sdk/include/reactos/undocshell.h

@@ -697,6 +697,7 @@ SHInvokePrivilegedFunctionW(
 
 BOOL WINAPI
 SHTestTokenPrivilegeW(_In_opt_ HANDLE hToken, _In_z_ LPCWSTR lpName);
+BOOL WINAPI IsSuspendAllowed(VOID);
 
 /*****************************************************************************
  * Shell32 resources