Add IPv6 support in RestTemplate

Prior to this commit, RestTemplate would not would
not accept IPv6 raw addresses in URLs because UriComponentsBuilder
would not parse/encode the Host part correctly.

The UriComponentsBuilder now parses and encode raw IPv6 addresses
in the "[1abc:2abc:3abc::5ABC:6abc]" format and also supports the
use of IPv6 scope_ids (see JDK8 java.net.Inet6Address),
like "[1abc:2abc:3abc::5ABC:6abc%eth0]".

Issue: SPR-10539