Proxy.supportsHostname

Some proxy protocols expect to be passed a hostname, which they will resolve to an IP address themselves. Others, like SOCKS4, do not allow this. This function will return false if proxy is implementing such a protocol. When false is returned, the caller should resolve the destination hostname first, and then pass a #GProxyAddress containing the stringified IP address to [gio.proxy.Proxy.connect] or [gio.proxy.Proxy.connectAsync].