logging: Log Info messages unconditionally

Summary:
Previously Info-level logging when a category was specified (via
LogPrintLevel) would only print the corresponding log message if
-debug=category were specified, while Info-level logging without a
category would always be printed. Make this more consistent by having
Info messages always be logged, whether they include a category or not.

This is a partial backport of core#28318 and core#29230
https://github.com/bitcoin/bitcoin/pull/28318/commits/ab34dc6012351e7b8aab871dd9d2b38ade1cd9bc
Depends on D18270

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18271