vnc: move initialization to framebuffer_update_request

qemu sends various state info like current cursor shape to newly connected
clients in response to a set_encoding message.  This is not correct according
to the rfb spec.  Send that information in response to a full (incremental=0)
framebuffer update request instead.  Also send the resize information
unconditionally, not only in case of an actual server-side change.

This makes the qemu vnc server conform to the spec and allows clients to
request the complete vnc server state without reconnect.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20210112134120.2031837-3-kraxel@redhat.com