She’s young, she just moved into the district and she is taking on an established and popular House Democrat in a primary bid she concedes is a huge gamble. She’s also a hedge fund lawyer, and proud of it. All that may not exactly excite liberal primary voters. But Reshma Saujani, 34, has won the backing of some prominent Democratic donors for her bid to topple Representative Carolyn B. Maloney, a challenge that is turning heads on the Upper East Side of Manhattan and antagonizing some of New York’s best-known feminists. It is a campaign steeped in identity politics —...