mathlib3

3b55b948 - feat(analysis/inner_product_space/basic): inner products of linear combinations of orthonormal vectors (#11323)

feat(analysis/inner_product_space/basic): inner products of linear combinations of orthonormal vectors (#11323) There are some lemmas about the inner product of a linear combination of orthonormal vectors with one vector from that orthonormal family. Add similar lemmas where both sides of the inner product are linear combinations.