Under gtk/gtk3 we send CommandEventId::ModKeyChange on
key down, to support the auto-accelerator feature. But
at least the handler in SwEditWin::Command must get it
on key up, in order to not interfere with other
ctrl+shift+X shortcuts, which work on key down.

To achieve that, we need:

- On key up pass the key that was just released, instead
  of the current state of nothing being pressed.

- Have a flag of whether it's a key down or up event, so
  it can be checked by the application code.

Change-Id: If188d6ccdc3b214a2c3ed20aad291d74d46b358f
Reviewed-on: https://gerrit.libreoffice.org/37275Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Maxim Monastirsky <momonasmon@gmail.com>