Blackstone, the world’s largest alternative asset management firm, is all-in on Manhattan’s turnaround after the COVID pandemic crippled the commercial real estate market. The firm’s effort to buy 1345 Sixth Ave. from Fisher Brothers was widely hailed this week as a stroke of faith in the Manhattan office market — but it wasn’t the first mega-deal by the financial giant. Last summer, Stephen A. Schwarzman-led Blackstone also signed the largest…
