[dev.typeparams] go/types: disallow type list handling
This is a port of CL 324571 to go/types, though type list handling is
guarded by a const rather than a config option.
Change-Id: I91c940fead048980603e0bb56fcc896dbef4f94c
Reviewed-on: https://go-review.googlesource.com/c/go/+/326683
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@golang.org>