core, core/rawdb, eth/sync: no tx indexing during snap sync (#28703)

This change simplifies the logic for indexing transactions and enhances the UX when transaction is not found by returning more information to users.

Transaction indexing is now considered as a part of the initial sync, and `eth.syncing` will thus be `true` if transaction indexing is not yet finished. API consumers can use the syncing status to determine if the node is ready to serve users.

ethstats/ethstats.go

@@ -792,7 +792,7 @@ func (s *Service) reportStats(conn *connWrapper) error {
 		}
 
 		sync := fullBackend.SyncProgress()
-		syncing = fullBackend.CurrentHeader().Number.Uint64() >= sync.HighestBlock
+		syncing = !sync.Done()
 
 		price, _ := fullBackend.SuggestGasTipCap(context.Background())
 		gasprice = int(price.Uint64())
@@ -801,7 +801,7 @@ func (s *Service) reportStats(conn *connWrapper) error {
 		}
 	} else {
 		sync := s.backend.SyncProgress()
-		syncing = s.backend.CurrentHeader().Number.Uint64() >= sync.HighestBlock
+		syncing = !sync.Done()
 	}
 	// Assemble the node stats and send it to the server
 	log.Trace("Sending node details to ethstats")