McKINNEY, Texas—Scottie Scheffler is looking up on the leaderboard at the AT&T Byron Nelson at a couple of contemporaries without nearly the resume the Dallas resident has built over the past 15 months. In fact, Austin Eckroat and China’s Marty Dou are seeking a first PGA Tour victory. The Oklahoma-raised Eckroat shot an 8–under 63,…