April should bring big share-price swings to these very different businesses.Growth stock investors have had an epic run this year thanks to the rally that pushed the tech-heavy Nasdaq Composite index up 33% over the past 12 months. Nvidia and Meta Platforms more than doubled in that time, making them two of the most explosive gainers in a rising market.Indexes may turn lower following such a huge spike, of course. But markets also have a way of booking a string of fresh records when momentum is this strong ...