The Kingdom’s Public Investment Fund is teaming with Related Cos., which has said it is planning to build a 1,200-foot tower on a site one block from Central Park, which was purchased last year for more than $600 million. Related initially planned a mixed-use project there with residential, retail and a hotel. But more recently the firm said it has been considering an office building instead to take advantage of the strong demand among businesses for top-quality space in the city. The overall cost for the site and development is expected to be more than $1 billion.