“Mulan” hits Disney+ on Friday, viewers just might tear up when they hear a familiar ballad sung by a famous voice during the end credits: “Reflection” by Christina Aguilera.Now 39, the pop star is once again taking on the tune that made her famous when she was little more than a 17-year-old former Disney Mouseketeer. Aguilera’s revamped rendition has garnered more than 6 million views since being posted Aug.