refactor: remove usage of locale dependent std::isspace

Summary:
Don't rely on locale dependent functions in base_blob<BITS>::SetHex(...)
(uint256), DecodeBase58(...), ParseMoney(...) and ParseHex(...)

Backport of core PR14585

Depends on D2698

Test Plan:

./test/lint/lint-locale-dependence.sh

Ensure there is no output

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2706