WebRTC IPv6 support for TURN (along with REQUESTED-ADDRESS-FAMILY)

[ha-ves]

This PR is for supporting IPv6. (and adding obsolescence warnings for RFC 3489)

Summary:

• [x] Added REQUESTED-ADDRESS-FAMILY attribute type for Allocation Request and Refresh Request according to RFC 8656,
• [x] Added STUNAddressAttributeBase abstract class for better code management,
• [x] Added IP AddressFamily determination at creation and parsing time,
• [x] IPv6 support for XOR-d (encoded) IP Address according to RFC 8489 (section 14.2),
  • [x] Using STUNHeader.TransactionId,
  • [ ] But I didn't add IPv6 support for RFC 3489 though... as commented in RFC 5389 (section 15.1),
• [ ] Should work for both TURN client and TURN server modes (?) (not tested yet for turn server mode),
• [x] Added deprecated warnings for RFC 3489 MAPPED-ADDRESS STUNAddressAttribute attribute usage

[ha-ves]

Will improve for #616, along with that case, might add a future PR for transport type.