[release-branch.go1.18] go/types, types2: allow (string...) signature with NewSignatureType
Includes cases where the core type of the variadic parameter is
a slice or bytestring. Permits a client to create the signature
for various instantiations of append.
Fixes #55148.
Change-Id: I0f4983eb00c088cbe1d87954ee0b2df0ccc3bc49
Reviewed-on: https://go-review.googlesource.com/c/go/+/430455
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Robert Griesemer <gri@google.com> Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/431915