os: implement fs.StatFS for os.DirFS
os: implement fs.StatFS for os.DirFS

Change-Id: I1d7382bf522aeda7148431b348f6ab9a162be097
Reviewed-on: https://go-review.googlesource.com/c/go/+/304531
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Trust: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

cloudflare/go,golang/go,golang/go,nawawi/go,nawawi/go,CAFxX/go,golang/go,cloudflare/go,nawawi/go,golang/go,CAFxX/go,cloudflare/go,nawawi/go,cloudflare/go,nawawi/go,nawawi/go,golang/go,CAFxX/go,golang/go,CAFxX/go,cloudflare/go,golang/go,cloudflare/go,CAFxX/go,CAFxX/go,cloudflare/go,CAFxX/go,nawawi/go,cloudflare/go,CAFxX/go,golang/go,nawawi/go