chore(algebra/big_operators): reorder the definitions in `norm_num` extension (#15840)
chore(algebra/big_operators): reorder the definitions in `norm_num` extension (#15840)

This prepares for PR #15538, where `eval_finset` calls `eval_multiset`, which calls `eval_list`.
By reordering in a separate PR, we get a cleaner diff.







leanprover-community/mathlib,leanprover-community/mathlib