refactor: make EncodeBase58{Check} consume Spans

Summary:

util: make EncodeBase58 consume Spans

util: make EncodeBase58Check consume Spans

This is a backport of core#19706

No change was necessary in bench/base58.cpp, because we already use vectors (D1857).
In guiutil.cpp, we use EncodeCashAddr.

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10114