Note that multi{set,map}::emplace doesn't specify in which order the new element is inserted if there are equivalent keys in the table, whereas emplace_hint specifies that the new element must be before the hint if possible.
https://en.cppreference.com/w/cpp/container/multiset/emplace
https://en.cppreference.com/w/cpp/container/multiset/emplace_hint

Also refactor to rely on IsAssertEnabled instead of checking for NDEBUG.

PiperOrigin-RevId: 486733450
Change-Id: Ie90d33c584a6caccd8301ad6fc0396234dbbfac4