mathlib3

4e24f4cf - feat(data/list/*): add indexed versions of some list functions (#2191)

feat(data/list/*): add indexed versions of some list functions (#2191) Add `foldr_with_index`, `foldl_with_index`, `mfoldr_with_index`, `mfoldl_with_index`, `mmap_with_index` and `mmap_with_index'`. The new functions are proven correct by relating them to their non-indexed counterparts. Co-authored-by: Vierkantor <Vierkantor@users.noreply.github.com>