In a sprawling office in Hefei, the eastern Chinese electric vehicle hub, hundreds of employees and several robotic arms sat refining software developed jointly by German behemoth Volkswagen and Chinese EV maker XPeng. The days when foreign firms saw such partnerships largely as a necessary entrance fee to the world's largest auto market are long gone. Legacy overseas brands are now seeking out collaboration, hoping the domestic market's blistering pace and technological innovation will rub off and boost their competitiveness in China and increasingly, abroad. VW-XPeng's China Electronic Architecture (CEA) — software that controls a car's electronics — was delivered…