Fix Trac #9071, an egregious bug in TcDeriv.inferConstraints
The constraints for Functor don't line up 1-1 with the arguments (they are fetched out from sub-terms of the type), but the surrounding code was mistakenly assuming they were in 1-1 association. (cherry picked from commit 13a330e8) Conflicts: compiler/typecheck/TcDeriv.lhs
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