virtio-serial-bus: add terminal resize messages

Implement the part of the virtio spec that allows to notify the virtio
driver about terminal resizes. Gate the new resize support behind the
console-size property, which defaults to off. To implement the property,
restore VirtIOSerial::host_features (previously removed by commit
d0660e5b7fc7e97926232d13d2500a16df32b310).

The virtio spec contains two methods to inform the guest about console
size:

For legacy drivers, we have only one port and we put the terminal size
in the config space and inject the config changed interrupt.

For multiport devices, we use the control virtqueue to send a
packet containing the terminal size. Unfortunately, old versions
of the Linux kernel used an incorrect order for the fields (rows
then cols instead of cols then rows), until it was fixed by commit
5326ab737a47278dbd16ed3ee7380b26c7056ddd. As a result, when running an
old guest kernel, the number of rows and columns will be swapped.

Based on a patch originally written by Szymon Lukasz <noh4hss@gmail.com>,
but partially rewritten to fix various corner cases.

Signed-off-by: Szymon Lukasz <noh4hss@gmail.com>
Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20261012-console-resize-v10-11-2c3b10d829b3@gmail.com>