Broadway star Kelli Rabke, a singer-actress of petite stature, got to thinking; it occurred to her that an abundance of legendary singing stars, particularly those who've even become iconic, have been (or are) under 5'2″ in height. Thus was born her eye-opening and quite delightful show, directed by Mark Waldrop, at The Green Room 42, Tiny Giants"Petite Powerhouses from Garland to Gaga! Ironically, introducing …