New York City has shelled out nearly $100 million in taxpayer dollars to rent more than two dozen buildings that were meant to house preschools — but have yet to open half a decade later, The Post has learned.  The city is still footing the rent and utility bills for the 28 facilities — a $99.3 million-and-counting boondoggle blamed on the “terrible execution” of former Mayor Bill de Blasio’s ambitious universal preschool expansion. “I don’t think it’s corruption. It’s incompetence,” a former