Move scheduling Heap in to scheduler.core.utils

The Heap data structure is useful for our backoff system in addition to
scheduling queue. Move it to somewhere it can be consumed by both
systems and properly export needed names. Also adding unit tests
from client-go/tools/cache/heap.go.

pkg/scheduler/internal/queue/scheduling_queue_test.go

@@ -199,7 +199,7 @@ func TestPriorityQueue_Update(t *testing.T) {
 	}
 	// Update highPriorityPod and add a nominatedNodeName to it.
 	q.Update(&highPriorityPod, &highPriNominatedPod)
-	if q.activeQ.data.Len() != 1 {
+	if q.activeQ.Len() != 1 {
 		t.Error("Expected only one item in activeQ.")
 	}
 	if len(q.nominatedPods) != 1 {
@@ -250,7 +250,7 @@ func TestPriorityQueue_MoveAllToActiveQueue(t *testing.T) {
 	q.unschedulableQ.addOrUpdate(&unschedulablePod)
 	q.unschedulableQ.addOrUpdate(&highPriorityPod)
 	q.MoveAllToActiveQueue()
-	if q.activeQ.data.Len() != 3 {
+	if q.activeQ.Len() != 3 {
 		t.Error("Expected all items to be in activeQ.")
 	}
 }