[tz] Changing 24:00 to 0:00 where possible

[Garrett Wollman]

<<On Tue, 04 Apr 2023 12:45:54 -0700, Brian Park via tz <tz at iana.org> said:

> I am curious to hear that your TZDB parsing is exposed to your
> end-users and is in the critical path. I would have thought that the
> parsing would be done offline (e.g. after each TZDB release), and
> the TZDB data would be converted into a different format that is
> more amenable to the computation that your code is performing.

Since the very beginning of this project, there has been a standard
parsed data format (now called "TZif") and the `zic` utility has been
shipped to do the parsing.  Indeed, for a long time, the behavior of
`zic` was the only specification of the human-readable data format.

Of course, this format was designed for easy access by the C standard
library routines and not by JavaScript, but it would in theory not be
difficult to modify the `zic` source code to generate a different
output format that was more amenable to document-processing languages.

-GAWollman