Thirteen years ago, High School Musical broke free from the crop of early-aughts Disney Channel originals and became something of a phenomenon, a clique-crossing tale of jocks and theater kids that launched Zac Efron into superstardom, a modern-day Romeo & Juliet but if Shakespeare swapped out the tragic double suicide for a catchy choreographed tune about putting aside your differences. For a very specific window of young-ish people, yours truly included, HSM is a potent nostalgia hit, which is what Disney+ is counting on when it returns to the title for High School Musical: The Musical: …