go/types, types2: flip message contents for reverse type inference errors

go/types, types2: flip message contents for reverse type inference errors

Add a new flag 'reverse' to control the formatting of type inference
error messages.

This change only impacts error messages.

Fixes #60747.

Change-Id: I81e13075e3157252ccc09f358bd29bd676c34499
Reviewed-on: https://go-review.googlesource.com/c/go/+/549055
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>