Rulesave: Save description file, if it lives under ruleset directory
Originally meant for master-only, this was backportable all the way to S3_0.
CI rulesets_save.sh test fails with this. First save copies the description file, but resave does not (as it's not within "correct" directory at that point).
Split make_dir_for_file() part -> #46317
When the description file lives under the ruleset directory itself, ruleset should and could create a copy to the new ruleset directory being written.