[tlbuild] icu-57.1 trial builds in tl

[Karl Berry]

I just imported icu-57.1 (release) into the TL source tree, including
the same changes that were made by peb in the last round.  (A couple of
the patches had been applied, but most were still needed.)  I also cut
down the huge .dat file in (I hope) the same way.

Since icu has historically been a common cause of build problems in
multifarious unexpected ways, please give it a try.

I don't know where luatex stands.  I think the other principal programs
are pretty much stable, though who knows ...

Thanks,
Karl