cmd/go/internal/work: make formatOutput return an error that includes the import...

cmd/go/internal/work: make formatOutput return an error that includes the import path

This refines the error output that was previously adjusted in CL 437298.

Longer term, we should consider unraveling the call chains involving
formatOutput to avoid passing so many parameters through so many
different formatting functions.

Updates #25842.

Change-Id: I3b9d03bf5968902d8ccc4841ab4dbe114a2239e4
Reviewed-on: https://go-review.googlesource.com/c/go/+/451218
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>