In a development that would have seemed unlikely as recently as a decade ago, and that has significant implications for the vitality of Boston theater, talented young performers increasingly see Boston as a place to forge an acting career, not just to launch one. “It’s more than a steppingstone,’’ asserts Daniel Berger-Jones, 28, who graduated from Boston University and is one of a group of young actors who founded the Orfeo Group, a small and adventurous theater company. “We are developing a nice culture here.’’