Previously the only Ifs that were typed unreachable were those in which both arms were unreachable and those in which the condition was unreachable that would have otherwise been typed none. This caused problems in IRBuilder because Ifs with unreachable conditions and value-returning arms would have concrete types, effectively hiding the unreachable condition from the logic for dropping concretely typed expressions preceding an unreachable expression when finishing a scope. Relax the conditions under which an If can be typed unreachable so that all Ifs with unreachable conditions or two unreachable arms are typed unreachable. Propagating unreachability more eagerly this way makes various optimizations of Ifs more powerful. It also requires new handling for unreachable Ifs with concretely typed arms in the Printer to ensure that printed wat remains valid. Also update Unsubtyping, Flatten, and CodeFolding to account for the newly unreachable Ifs.