go/types, types2: avoid sorting all errors when matching errors

go/types, types2: avoid sorting all errors when matching errors

Sorting is only needed if there are multiple matching errors on
the same line. Instead, in that rare case, select the error that
is closest.

Follow-up on CL 456137.

Change-Id: Ia2056b21c629f3a42495e32de89607fbefb82fa7
Reviewed-on: https://go-review.googlesource.com/c/go/+/456335
Run-TryBot: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>