[dev.typeparams] cmd/compile/internal/types2: fix range over exprs of type parameter type
For range expressions of type parameter type, the structural type
of the type parameter's constraint determines the range operation.
While at it, rename implicitArrayDeref to arrayPtrDeref.
Change-Id: Ib631a8a14e717498e5264944f659309df1f68cc2
Reviewed-on: https://go-review.googlesource.com/c/go/+/339897
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Robert Findley <rfindley@google.com>