New York City Mayor Bill de Blasio has announced $8.2 billion in public funds for a 10-year housing plan aimed at providing affordable homes to thousands of low- to middle-income residents. The mayor intends to require developers to include affordable units in residential projects being developed in newly rezoned areas around the city. Mr. de Blasio said that with $2.9 billion in state and federal money and more than $30 billion the city expects to attract in private funds, the projected investment to create and maintain affordable units will total more than $41.1 billion over 10 years. But there could be a downside — the requirement can reduce profits and dissuade developers from building.