State immunity — State agency — Commercial activity — Implied waiver of immunity — Claim for breach of contract and repayment of debt against foreign State and State agency — Application for security for costs — State entity established by decree to manage assets on insolvency of business based in that State — State entity participating in litigation relating to insolvency in United States courts without raising defence of State immunity — Whether an implied waiver — Whether liquidation and management of assets a commercial activity — Foreign Sovereign Immunities Act 1976 — Whether act of State doctrine applicable — The law of the United States