This error occurs when a module is loaded with one name (for example,
github.com/golang/lint) but declares a different path in its go.mod
(golang.org/x/lint). The current text "unexpected module path" is
confusing. It doesn't explain why the path was unexpected, and it's
not clear what was expected.

With this change, the error text includes the module and version
containing the go.mod file with the error, the declared module path,
and the loaded module path. The paths are vertically aligned so
differences are visually obvious. As with other module version errors,
the shortest chain of requirements is printed.

This change supercedes CL 158477.

Fixes #28489

Change-Id: Ieb07d00bcae182376d7be6aad111c84fbf784354
Reviewed-on: https://go-review.googlesource.com/c/go/+/185985
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>