Sovereign immunity — Foreign State-owned corporations — Nature of plea of immunity — Plea which goes to subject matter jurisdiction — Waiver of immunity — Whether to be inferred from dilatory conduct in raising and arguing plea — Restrictive theory — Commercial activity — Connection with the United States — Action for personal injuries against manufacturer of allegedly defective product — Agreement to arbitrate disputes in third State — Whether a waiver of immunity before United States courts — Foreign Sovereign Immunities Act 1976 — The law of the United States