Accept VNC passwords longer than 8 bytes

I'm aware of the reasons why passwords are limited by 8 bytes in VNC, but unfortunately, some server implementations have alternative authentication methods that accept longer passwords. RFB itself doesn't seem to mention the limit https://tools.ietf.org/html/rfc6143

For this reason, I would like to propose that we accept more bytes in the password_entry. By doing this, servers that accept up to 8 bytes will simply ignore/discard the rest of the string.

This has been requested downstream in https://bugzilla.redhat.com/1767963

And a fix would be a one-liner in https://gitlab.gnome.org/GNOME/vinagre/blob/master/plugins/vnc/vinagre-vnc-tab.c#L511

MacOS X seems to impose no limits on this. Remmina doesn't limit characters either.