go/types, types2: fix printing of error message with variadic calls
Distinguish between variadic signatures and argument lists to
(possibly variadic) functions and place `...` before or after
the last type in the list of types.
Fixes a panic.
Fixes #70526.
Change-Id: I77aba8f50984a21ebcdb62582030f2d0fe0eb097
Reviewed-on: https://go-review.googlesource.com/c/go/+/632275 Reviewed-by: Alan Donovan <adonovan@google.com>
Auto-Submit: Robert Griesemer <gri@google.com> Reviewed-by: Robert Findley <rfindley@google.com> Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>