[PSDK] Add GetMenuPosFromID() declaration in shlwapi.h

This function is exported from shlwapi.dll since version 4.71.
It has been publicly documented in MS PSDK and MSDN since at least
Windows XP/2003 and claimed to be declared in shlwapi.h; however,
this is inaccurate: it has been declared only starting Vista PSDK.

sdk/include/psdk/shlwapi.h

@@ -1907,6 +1907,8 @@ SHFreeShared(
 
 #endif /* NO_SHLWAPI_SHARED */
 
+INT WINAPI GetMenuPosFromID(_In_ HMENU hMenu, _In_ UINT uID);
+
 /* SHAutoComplete flags */
 #define SHACF_DEFAULT               0x00000000
 #define SHACF_FILESYSTEM            0x00000001