runtime/debug: add API to read module info in binary

When module is enabled, the go tool embeds build information
related to the module in the binary including the dependencies
and the replace information (See
src/cmd/go/internal/modload.PackageBuildInfo).

The newly introduced ReadBuildInfo reads the information and
makes it accessible programmatically.

Update #26404

Change-Id: Ide37022d609b4a8fb6b5ce02afabb73f04fbb532
Reviewed-on: https://go-review.googlesource.com/c/144220


Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>