design: type parameters: promote embedded methods from constraint
design: type parameters: promote embedded methods from constraint

Change-Id: If4be0f74932c1ec504833549fb01a047dcf8335f
Reviewed-on: https://go-review.googlesource.com/c/proposal/+/251444
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

golang/proposal,golang/proposal