cmd/go: compute BuildInfo and EmbedFiles when listing export data

cmd/go: compute BuildInfo and EmbedFiles when listing export data

'go list -export' lists the locations of compiled artifacts,
so it needs to load all of the metadata needed to compile each package.

Fixes #58885.

Change-Id: Ie78527e0fb423698fb4195fe50e0b6925b05aa8c
Reviewed-on: https://go-review.googlesource.com/c/go/+/477197
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>