NEW YORK — Jury selection and opening statements were set to begin Monday in a trial that mashes up Ed Sheeran’s “Thinking Out Loud” with Marvin Gaye’s “Let’s Get It On.”The heirs of Ed Townsend, Gaye’s co-writer of the 1973 soul classic, sued Sheeran, alleging the English pop star’s hit 2014 tune has “striking similarities” to “Let’s Get It On” and “overt common elements” that violate their copyright.The lawsuit filed in …