mathlib3

38375881 - feat(linear_algebra/affine_space/independent): `affine.simplex.reindex` (#17566)

feat(linear_algebra/affine_space/independent): `affine.simplex.reindex` (#17566) Add a definition for remapping a simplex along an `equiv` of index types, and associated basic API. (Typically of course the two index types are defeq and this is a permutation of indices within the same type, but the definition covers the general case where they might not be defeq.)