common,w32: Allow Unicode input and output with the console.

* common/ttyio.c (do_get) [W32]: Use ReadConsoleW.
(w32_write_console): New.
(tty_printf, tty_fprintf) [W32]: Use new function.

Note that due this change fixed stings (i.e. gettext translations)
printed to the console will not be rendered correctly unless "chcp
65001" has been used. This needs to be fixed by followup patch.

• GnuPG-bug-id: T4365