Seeing David Henry Hwang and Jeanine Tesori jaywalk across Geary Street unencumbered by an entourage, you might not peg them as the creators of the most anticipated new show on the West Coast. Their play, “Soft Power,” opened the night before in Los Angeles to raves, and the two seemed giddy at this affirmation of four years of toil, with Hwang supplying the book and lyrics and Tesori the music.