embed: implement openFile.ReadAt
Implementation copied from testing/fstest/mapfs.go
Fixes #57803
Change-Id: I531682b50ab6663511bac41fce7614ab9197bf38
GitHub-Last-Rev:
d9bcc1c0bf4d339edcdabaf4d4d67b848ad8818d
GitHub-Pull-Request: golang/go#59489
Reviewed-on: https://go-review.googlesource.com/c/go/+/483235
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: David Chase <drchase@google.com>