[tz] Leap Second Support Interval Field Request - RFC8536

[Michael H Deckers]

    On 2019-12-06, Arthur David Olson proposed
    a method to expose in TZif the expiration date
    of the leap second information:


> One odd possibility below.
>
>      @dashdashado
>
> Zone    Etc/Leapendstat 0       -       PRE     2020 Jun 28
>                          0       -       POST
>


    Why not produce a tzdb Zone for TAI? As if we had

        Zone    Etc/TAI  0:00:10 -      TAI     1972 Jul  1
                         0:00:11 -      TAI     1973 Jan  1
                         ....
                         0:00:35 -      TAI     2015 Jul  1
                         0:00:36 -      TAI     2017 Jan  1
                         0:00:37 -      TAI     2020 Jun 28
                         0:00:37 -      N_A

    After all, the Bulletins C of the IERS specify TAI as
    a function of UTC, just like a tzdb "timezone".

    Michael Deckers.