Move GetTopic function out of runc shim

Every shim implementation needs to select a correct publisher topic when posting events, so move it out of Linux-only runc code to the place where other shims can also use it

Otherwise, shims have to copy-paste this code. For example, see runj: 8158e558a3/containerd/shim.go (L144-L172)

Signed-off-by: Marat Radchenko <marat@slonopotamus.org>

runtime/v2/runc/task/service.go

@@ -42,6 +42,7 @@ import (
 	"github.com/containerd/containerd/pkg/userns"
 	"github.com/containerd/containerd/protobuf"
 	ptypes "github.com/containerd/containerd/protobuf/types"
+	"github.com/containerd/containerd/runtime"
 	"github.com/containerd/containerd/runtime/v2/runc"
 	"github.com/containerd/containerd/runtime/v2/runc/options"
 	"github.com/containerd/containerd/runtime/v2/shim"
@@ -687,7 +688,7 @@ func (s *service) forward(ctx context.Context, publisher shim.Publisher) {
 	ns, _ := namespaces.Namespace(ctx)
 	ctx = namespaces.WithNamespace(context.Background(), ns)
 	for e := range s.events {
-		err := publisher.Publish(ctx, runc.GetTopic(e), e)
+		err := publisher.Publish(ctx, runtime.GetTopic(e), e)
 		if err != nil {
 			log.G(ctx).WithError(err).Error("post event")
 		}