AK: Add IPv6Address class

This is the IPv6 counter part to the IPv4Address class and implements
parsing strings into a in6_addr and formatting one as a string. It
supports the address compression scheme as well as IPv4 mapped
addresses.

Tests/AK/CMakeLists.txt

@@ -32,6 +32,7 @@ set(AK_TEST_SOURCES
     TestHashTable.cpp
     TestHex.cpp
     TestIPv4Address.cpp
+    TestIPv6Address.cpp
     TestIndexSequence.cpp
     TestIntegerMath.cpp
     TestIntrusiveList.cpp