ASML Holdings NV’s €1.3 billion investment in Mistral gives the French startup a valuable dose of capital and credibility as it seeks to build an artificial-intelligence champion for Europe. Yet Mistral still has to prove it can survive in an industry dominated by much larger American and Chinese competitors.The Paris-based company’s valuation will rise to €11.7 billion as part of the ASML-led funding round, putting it among the most valuable private companies in Europe just two and a half years...