go/types, types2: better error messages for invalid calls
Rather than reporting "non-function" for an invalid type parameter,
report which type in the type parameter's type set is not a function.
Change-Id: I8beec25cc337bae8e03d23e62d97aa82db46bab4
Reviewed-on: https://go-review.googlesource.com/c/go/+/654475 Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com> Reviewed-by: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>