“Everybody’s Talking About Jamie” is an enjoyable escape from COVID-19 doldrums in L.A. The amiable musical, which opened last weekend at the Ahmanson Theatre, is sure to have people humming catchy choruses on the way home. “Everybody’s Talking About Jamie” could easily be dismissed as another high school musical about teen angst. It mines familiar territory with a main character who does not fit in trying to overcome bullies and naysayers. “The Prom” and “Dear Evan Hansen” are two recent examples. The premise may be trite, but “Jamie” the musical and Jamie, the title character, defy expectations. The cast is wonderful and the celebratory show…