function add(coordinate, delta) {
  coordinate[0] += +delta[0];
  coordinate[1] += +delta[1];
  return coordinate;
}
Add `delta` to `coordinate`. `coordinate` is modified in place and returned
by the function.

Example:

    import {add} from 'ol/coordinate.js';

    const coord = [7.85, 47.983333];
    add(coord, [-2, 4]);
    // coord is now [5.85, 51.983333]

@param {Coordinate} coordinate Coordinate.
@param {Coordinate} delta Delta.
@return {Coordinate} The input coordinate adjusted by
the given delta.
@api