mathlib3

e1452ef2 - chore(number_theory/legendre_symbol/*): move zmod.{legendre|jacobi}_sym* to other namespaces (#16461)

chore(number_theory/legendre_symbol/*): move zmod.{legendre|jacobi}_sym* to other namespaces (#16461) This PR moves `legendre_sym` and `jacobi_sym` (and `qr_sign`) to the root namespace. It also moves definitions and lemmas named `legendre_sym_...` to the `legendre_sym` namespace and analogous for `jacobi_sym_...` and `qr_sign_...`. We change names like `jacobi_sym_two` to `jacobi_sym.at_two`. This mostly affects the files `number_theory.legendre_symbol.quadratic_reciprocity` and `number_theory.legendre_symbol.jacobi_symbol`. Note that names like `exists_sq_eq_neg_one_iff` have been left in `zmod`. We prefix `quadratic_reciprocity*` by `legendre_sym` to disambiguate with the versions for the Jacobi symbol. (The links in `docs/100.yaml` and `docs/overview.yaml` are updated accordingly.) We also move the results in `number_theory.legendre_symbol.gauss_eisenstein_lemmas` from the `legendre_symbol` namespace to the `zmod` namespace. See this [Zulip thread](https://leanprover.zulipchat.com/#narrow/stream/116395-maths/topic/Jacobi.20symbol/near/297792676) and the comments at [#16395](https://github.com/leanprover-community/mathlib/pull/16395) for discussion.