Labeled metabolites of polycyclic aromatic hydrocarbons. VI. Trans‐7,8‐dihydrobenzo[a]pyrene‐7,8,diol‐G‐3H and (±)‐7α,8β‐dihydroxy‐9β,10β‐epoxy‐7,8,9,10‐tetrahydrobenzo[a]pyrene‐G‐3H