go/types, types2: separate formatting from error handling functions
This change moves formatting-specific functionality into a new file
format.go and rearranges the code in the errors.go files to be in
the same order for go/types and types2, making them more similar.
No functionality change. This is a pure code reordering.
Change-Id: Ibd818792397be146ad510a6c7308c85d3bb65956
Reviewed-on: https://go-review.googlesource.com/c/go/+/566555
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Robert Griesemer <gri@google.com> Reviewed-by: Robert Findley <rfindley@google.com> Reviewed-by: Robert Griesemer <gri@google.com>