go/types, types2: reorder object processing to avoid broken aliases

By processing non-alias type declarations before alias type declaration,
and those before everything else we can avoid some of the remaining
errors which are due to alias types not being available.

For #25838.
For #50259.
For #50276.
For #50729.

Change-Id: I233da2899a6d4954c239638624dfa8c08662e6b9
Reviewed-on: https://go-review.googlesource.com/c/go/+/380056


Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>