Fix missing unboxed tuple RuntimeReps (#16565)

Unboxed tuples and sums take extra RuntimeRep arguments,
which must be manually passed in a few places.
This was not done in deSugar/Check.

This error was hidden because zipping functions in TyCoRep
ignored lists with mismatching length. This is now fixed;
the lengths are now checked by calling zipEqual.

As suggested in #16565, I moved checking for isTyVar and
isCoVar to zipTyEnv and zipCoEnv.