Improve support of simplify_option_eq (and simplify_map_eq?) for setoids

Some testcases:

• https://gitlab.mpi-sws.org/FP/LambdaRust-coq/commit/c6a626adbe1bf78b34f4e74204b98007f532892d#59b3a9376af7e8ce6a745e02cef554707e5c7419_585_585
• in lambdaRust, lifetime/primitive.v, proof of own_ilft_auth_agree