[WIN32SS:NTUSER] Use the 2nd parameter of NtUserGetThreadDesktop() as fallback. ...

[WIN32SS:NTUSER] Use the 2nd parameter of NtUserGetThreadDesktop() as fallback. (#1065)

- The 2nd parameter is already passed in user-mode by GetThreadDesktop().
  It is then used by NtUserGetThreadDesktop() as a fallback for console
  threads.

- Lookup and validate the thread by using the IntTID2PTI() helper.
- Don't reference the desktop with too many access rights.
- Get rid of the old-school DECLARE_RETURN() & co. macros.

Co-authored-by: Hermès Bélusca-Maïto <hermes.belusca-maito@reactos.org>