“There’re not that many pieces — American pieces, at least — for soprano and orchestra,” said David Carlson of The Promise of Time, his new work to be sung by Christine Brewer at its world premiere by Marin Symphony, April 11 and 13. It will be the focal point, in the words of Marin Symphony Music Director Alasdair Neale, for a remarkable program, opening with Samuel Barber’s Essay for Orchestra N