The main function in log-validator is overly big, so this refactors it
in preparation for adding support for file globs, which is started in
the (currently draft) #7134
This PR should be functionally a no-op, except for one change:
The 1-per-second ratelimiter is moved to be per-file, so it's
1-per-second-per-file. I think this more closely aligns with what we'd
want, as we could potentially miss that a file had bad lines in it if it
was overwhelmed by another log file at the same time.
Matthew McPherrin