SAN DIEGO — Imagine if a team traded for Mike Clevinger, Blake Snell, Fernando Tatis Jr. and a handful of quality relief pitchers in the next several weeks. “Tati,” Drew Pomeranz said with a laugh. “That’s a franchise player. You can’t even trade for a guy like that.” Well, that is essentially the equivalent of what the Padres anticipate doing between now and the end of June. Clevinger on Wednesday made his first start since November 2020 Tommy John surgery, a return delayed at the start of this season by a right knee sprain. A half-dozen other players are due to come off the injured list, bol…