feat(analysis/inner_product_space/pi_L2): `map_isometry_euclidean_of_orthonormal` (#11907)
feat(analysis/inner_product_space/pi_L2): `map_isometry_euclidean_of_orthonormal` (#11907)

Add a lemma giving the result of `isometry_euclidean_of_orthonormal`
when applied to an orthonormal basis obtained from another orthonormal
basis with `basis.map`.







leanprover-community/mathlib,leanprover-community/mathlib