gnetworkaddress: fix parsing of URIs with IPv6 literal and port

Addresses like "http://[::1]:8080/" were being parsed as though they
did not include a port. Fix that, and add some more parsing tests.
gnetworkaddress: allow IPv6 scope ids in URIs

GNetworkAddress was allowing IPv6 scope ids in g_network_address_new()
/ g_network_address_parse(), but not in g_network_address_parse_uri().
Fix that.

Part of https://bugzilla.gnome.org/show_bug.cgi?id=669724