refactor: remove usage of locale dependent std::isspace #14585

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

Rationale:

$ uname -s
Darwin
$ cat poc.cpp
#include <iostream>
#include <locale>

int main(void) {
    setlocale(LC_ALL, "");
    std::cout << std::isspace(133) << ' ' << std::isspace(154) << ' ' << std::isspace(160);
    std::cout << '\n';
}
$ clang++ -o poc poc.cpp
$ ./poc
1 0 1
$ LC_ALL=en_US ./poc
1 0 1
$ LC_ALL=C ./poc
0 0 0
$ LC_ALL=ru_RU.KOI8-R ./poc # an "interesting" locale
0 1 0

<!--e57a25ab6845829454e8d69fc972939a-->Reviewers, this pull request conflicts with the following ones:

• #14555 (Move util files to directory by jimpo)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

utACK 15db77f4dd7f1a7963398f1576580b577a1697bc

utACK 15db77f

Could include a test comparing its output to std::isspace

utACK 15db77f

ACK 15db77f

Tested the same poc, other interesting locales:

LC_ALL=it_IT.ISO8859-15 ./poc
0 0 1
LC_ALL=uk_UA.KOI8-U ./poc
0 1 0
LC_ALL=hu_HU.ISO8859-2 ./poc
0 0 1