ui/win32-kbd-hook: handle AltGr in a hook procedure

ui/win32-kbd-hook: handle AltGr in a hook procedure

Import win32 keyboard hooking code from project spice-gtk. This
patch removes the extra left control key up/down input events
inserted by Windows for the right alt key up/down input events
with international keyboard layouts. Additionally there's some
code to grab the keyboard.

The next patches will use this code.

Only Windows needs this.

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Message-id: 20200516072014.7766-1-vr_qemu@t-online.de
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>