go/types: use error_.errorf for reporting related error information
Use error_.errorf for reporting related error information rather than
inlining the "\n\t". This aligns go/types with types2 in cases where the
related information has no position information. In other cases,
go/types needs to report a "continuation error" (starting with '\t') so
that users can access multiple error positions.
Change-Id: Ica98466596c374e0c1e502e7227c8d8c803b4c22
Reviewed-on: https://go-review.googlesource.com/c/go/+/400825
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@google.com>