By Greg Roumeliotis NEW YORK (Reuters) – Elon Musk clinched a deal to buy Twitter Inc for $44 billion cash on Monday in a transaction that will shift control of the social media platform populated by millions of users and global leaders to the world’s richest person. It is a seminal moment for the 16-year-old company, which emerged as one of the world’s most influential public squares and now faces a string of challenges. Musk, who calls himself a free speech absolutist, has criticized Twitter’s moderation. He wants Twitter’s algorithm for prioritizing tweets to be public and objects to giving…