[backport#15335] Fix lack of warning of unrecognized section names
Summary:
1a7ba84e11 Fix lack of warning of unrecognized section names (Akio Nakamura)
Pull request description:
In #14708, It was introduced that to warn when unrecognized section names are exist in the config file. But ```m_config_sections.clear()``` in ```ArgsManager::ReadConfigStream()``` is called every time when reading each configuration file, so it can warn about only last reading file if ```includeconf``` exists. This PR fix lack of warning by collecting all section names by moving ```m_config_sections.clear()``` to ```ArgsManager::ReadConfigFiles()``` . Also add a test code to confirm this situation.
Tree-SHA512: 26aa0cbe3e4ae2e58cbe73d4492ee5cf465fd4c3e5df2c8ca7e282b627df9e637267af1e3816386b1dc6db2398b31936925ce0e432219fec3a9b3398f01e3e65
Depends on D5757
This is a backport of Core PR15335
Test Plan:
ninja check test_runner.py feature_config_args.py
Reviewers: deadalnix, #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D5758