cmd/go: make 'go version' apply to files

cmd/go: make 'go version' apply to files

Expand "go version" from printing just the version of the
go command itself to being able to print the version of any
go binary (when listed on the command line).

This is a simplified version of rsc.io/goversion, which will
now be deprecated in favor of "go version".

(Preparatory changes to runtime, cmd/go, and cmd/link
made this version information easier to find, allowing a
much simpler implementation than in rsc.io/goversion.)

Fixes #31624.

Change-Id: I5f6f5b8392ce86a617e32ce287f6bf2aceafccff
Reviewed-on: https://go-review.googlesource.com/c/go/+/173343
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>