SoftBank Group Corp.’s Arm Holdings Ltd. took a step toward what’s set to become the biggest US initial public offering of the year, a bet that the once-obscure designer of phone chips can flourish in the era of artificial intelligence computing. Most Read from Bloomberg In a long-awaited regulatory filing Monday, Arm said the offering is being led by Barclays Plc, Goldman Sachs Group Inc., JPMorgan Chase & Co. and Mizuho Financial Group Inc. The document listed 24 other underwriters below that top tier — with Morgan Stanley notably absent. A successful debut by Arm would provide a windfall for…