[WIP] sql,kv: add compact_engine_span for internal use

This sql builtin can be used to compact the key span for a
given (nodeID, storeID, rangeID), on a running node.

This is incomplete:
- there is a TODO to figure out how to convert from the
  rangeID to the range span in planner.go
- there are no tests.

Informs ##26068

Release note: None

pkg/kv/kvclient/kvcoord/dist_sender.go

@@ -460,6 +460,11 @@ func (ds *DistSender) FirstRange() (*roachpb.RangeDescriptor, error) {
 	return ds.firstRangeProvider.GetFirstRangeDescriptor()
 }
 
+// NodeDialer returns a Dialer.
+func (ds *DistSender) NodeDialer() *nodedialer.Dialer {
+	return ds.nodeDialer
+}
+
 // getNodeID attempts to return the local node ID. It returns 0 if the DistSender
 // does not have access to the Gossip network.
 func (ds *DistSender) getNodeID() roachpb.NodeID {