go/types: better position for invalid slice indices error
This is a port of CL 363671 from types2 to go/types. Also adjust the
error message to match types2 ("invalid" vs "swapped").
Change-Id: I662a73c915814fea14bfcb1ebde0fbf39589f022
Reviewed-on: https://go-review.googlesource.com/c/go/+/364902
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@golang.org>