cmd/compile: use t.AllMethods when sorting typesByString

For interface types, t.Methods contains only unexpanded method set, i.e
exclusive of interface embedding. Thus, we can't use it to detect an
interface contains embedding empty interface, like in:

	type EI interface{}

	func f() interface{ EI } {
		return nil
	}

At the time we generate runtime types, we want to check against the full
method set of interface instead.

Fixes #46386

Change-Id: Idff53ad39276be6632eb5932b76e855c15cbdd2e
Reviewed-on: https://go-review.googlesource.com/c/go/+/323649


Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>