The valid conversions consider the core types of operands, not just
their underlying type.
This also explains the valid arguments for unsafe.Slice which are
explained in terms of unsafe.Pointer conversions.
unsafe.SliceData simply refers to "slice argument" and we use
similar terminology elsewhere in the spec to denote values that
have a core type of slice (or any other type for that matter).
Leaving alone for now.
Fixes #64452.
Change-Id: I0eed3abbc0606f22358835e5d434f026fe0909c8
Reviewed-on: https://go-review.googlesource.com/c/go/+/551379
Auto-Submit: Robert Griesemer <gri@google.com> Reviewed-by: Robert Griesemer <gri@google.com> Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>