Use new connection IDs in IETF quic connection migration.

Feature is also guarded by "RVCM" connection option.
Also mark NEW_CONNECTION_ID_FRAME as retransmittable as it is a control frame type.

Protected by FLAGS_quic_reloadable_flag_quic_connection_migration_use_new_cid.

PiperOrigin-RevId: 372122692
Change-Id: I76005ba39f50fad976b8146bd34fb4687c4d2ba1
diff --git a/quic/core/quic_connection_stats.h b/quic/core/quic_connection_stats.h
index 06b7f58..c2a64ce 100644
--- a/quic/core/quic_connection_stats.h
+++ b/quic/core/quic_connection_stats.h
@@ -209,6 +209,10 @@
   // which was canceled because the peer migrated again. Such migration is also
   // counted as invalid peer migration.
   size_t num_peer_migration_while_validating_default_path = 0;
+  // Number of NEW_CONNECTION_ID frames sent.
+  size_t num_new_connection_id_sent = 0;
+  // Number of RETIRE_CONNECTION_ID frames sent.
+  size_t num_retire_connection_id_sent = 0;
 
   struct QUIC_NO_EXPORT TlsServerOperationStats {
     bool success = false;