go/types, types2: remove redundant calls to Named.resolve

go/types, types2: remove redundant calls to Named.resolve

The resolved status of a Named type should be owned by its API, and
callers should access resolved data via methods. Remove several
instances where Named.resolve is explicitly invoked, only to be followed
by a method that also resolves.

Also make two minor cleanups:
- Remove the tparams parameter to Checker.newNamed, as it was unused.
- Include position information when assertions fail, so that one doesn't
  need to go digging in the panicking stack to find the assertion
  location.

Updates #52728

Change-Id: Icbe8c89e9cfe02d60af7d9ba907eaebe1f00193e
Reviewed-on: https://go-review.googlesource.com/c/go/+/404874
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>