Rename usewallet to rpcwallet, and allow square brackets for ipv6 addresses

Summary:
Backport Core PR10883 and PR10812

2264236   Rename -usewallet to -rpcwallet
5c643241e [refactor] move SplitHostPort() into utilstrencodings
fe4fabaf1 [utils] allow square brackets for ipv6 addresses in bitcoin-cli

Closes T181

Test Plan: make check

Reviewers: deadalnix, matiu, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Subscribers: jasonbcox, teamcity

Maniphest Tasks: T181

Differential Revision: https://reviews.bitcoinabc.org/D1046