go/types: implement NewTypeList and use it instead of composite literals

Also, simplify a bit of code in predicates.go.

This is a backport of changes in CL 344615 that were made in addition
to the changes of the original CL 343933; it brings go/types in sync
with types2.

Change-Id: I14cd4d4704d29894d0fbb8d129744d65e332ad22
Reviewed-on: https://go-review.googlesource.com/c/go/+/344570


Trust: Robert Griesemer <gri@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>