internal/saferio: new package to avoid OOM

internal/saferio: new package to avoid OOM

Broken out of debug/pe. Update debug/pe to use it.

For #47653

Change-Id: Ib3037ee04073e005c4b435d0128b8437a075b00a
Reviewed-on: https://go-review.googlesource.com/c/go/+/408678
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dan Kortschak <dan@kortschak.io>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>