Ruby: Ensure order-dependent iteration uses an ordered map

Ruby: Ensure order-dependent iteration uses an ordered map

This patch fixes a bug in Ruby that caused non-deterministic
simulation when changing the underlying hash map implementation. The
reason is order-dependent behaviour in combination with iteration over
the hash map contents. The two locations where a sorted container is
assumed are now changed to make use of a std::map instead of the
unordered hash map.

With this change, the stats changes slightly and the follow-on
changeset will update the relevant statistics.