Don't allow resolving of std::string:s with embedded NUL characters.
Avoid using C-style NUL-terminated strings as arguments in the netbase interface
Add tests.
This is a backport of PR17754 [1/3]
https://github.com/bitcoin/bitcoin/pull/17754/commits/9574de86ad703ad942cdd0eca79f48c0d42b102b