[tz] Yet more historical data for Iran

[Paul Eggert]

Thanks for the further data on Iran.

Unfortunately the obvious patch to the "asia" file uncovered what 
appears to be a longstanding bug in zic.c. So I installed the attached 
three patches to fix this.

The first patch refactors zic.c as I had trouble following its 
local-variable reuse, which is no longer needed with today's compilers.

The second patch fixes the zic.c bug in two different ways, sort of a 
belt-and-suspenders thing.

The third patch updates the "asia" file to reflect our latest 
understanding of Iran's civil time history, with a workaround to avoid 
the bug in zic 2022a and earlier.

PS. Sorry about misspelling your name in the last commit message.
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