Add in support for segmented binary stream snapshots.

Streams with many interior deletes was causing issues due to the fact that the interior deletes were represented as a sorted []uint64.
This approach introduces 3 sub types of delete blocks, avl bitmask tree, a run length encoding, and the legacy format above.
We also take into account large interior deletes such that on receiving a snapshot we can skip things we already know about.

Signed-off-by: Derek Collison <derek@nats.io>

server/jetstream_cluster_3_test.go

@@ -4519,3 +4519,25 @@ func TestJetStreamClusterSnapshotAndRestoreWithHealthz(t *testing.T) {
 	require_NoError(t, err)
 	require_True(t, si.State.Msgs == uint64(toSend))
 }
+
+func TestJetStreamBinaryStreamSnapshotCapability(t *testing.T) {
+	c := createJetStreamClusterExplicit(t, "NATS", 3)
+	defer c.shutdown()
+
+	nc, js := jsClientConnect(t, c.randomServer())
+	defer nc.Close()
+
+	_, err := js.AddStream(&nats.StreamConfig{
+		Name:     "TEST",
+		Subjects: []string{"foo"},
+		Replicas: 3,
+	})
+	require_NoError(t, err)
+
+	mset, err := c.streamLeader(globalAccountName, "TEST").GlobalAccount().lookupStream("TEST")
+	require_NoError(t, err)
+
+	if !mset.supportsBinarySnapshot() {
+		t.Fatalf("Expected to signal that we could support binary stream snapshots")
+	}
+}