“Soft Power”, David Henry Hwang and Jeanine Tesori’s dramaturgically breathtaking new musical-within-a-play, experiments with form while rendering a sort of reverse version of “The King and I”.  The resulting satire of American culture and politics brims with an unpretentious intelligence and an unexpectedly penetrating sense of patriotism.  If democracy will break your heart, “Soft Power” can mend it.