io: add a new ReadSeekCloser interface
Research showed that this interface is defined frequently enough in
real-world usage to justify its addition to the standard library.
Fixes #40962
Change-Id: I522fe8f9b8753c3fa42ccc1def49611cf88cd340
GitHub-Last-Rev:
6a45be66b42e482a06d9809d9da20c195380988b
GitHub-Pull-Request: golang/go#41939
Reviewed-on: https://go-review.googlesource.com/c/go/+/261577
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Trust: Dmitri Shuralyov <dmitshur@golang.org>