Harvard University’s investment arm disclosed a $2.2 billion stake in SpaceX, revealing a massive payoff from an early investment in Elon Musk’s rocket company following its blockbuster public debut.Harvard Management Company reported the position in a regulatory filing Friday, making SpaceX the largest individual stock holding disclosed in its $4.3 billion portfolio of U.S. equities.The investment highlights how SpaceX’s record-setting June initial public offering delivered significant gains for university endowments that gained exposure to the company through venture capital investments, in...