crypto/x509: update bundled iOS roots and rewrite generator

crypto/x509: update bundled iOS roots and rewrite generator

Switched the generator to using the open source releases of the root
store rather than HTML parsing, while trying to emulate the sorting
algorithm of the table to reduce churn.

Updates #38843

Change-Id: I78608d245eabc2a35c2f98635ed5f1a531ad2ba8
Reviewed-on: https://go-review.googlesource.com/c/go/+/239557
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>