Whatever you say about Dexter Fletcher’s glossy, glittering Elton John blinged-out biopic “Rocketman,” a shiny sequin of a movie, it doesn’t lack for sparkle. Almost slavishly sealed within the hermetic bubble of the rock biopic, “Rocketman” will, justifiably, draw plenty of comparisons to its opening act: last year’s Freddie Mercury tale “Bohemian Rhapsody.” They’re both about larger-than-life figures, each gay …
