Use batch inversion in precomputations

- Add secp256k1_ge_set_all_gej method to convert a batch of jacobian points to affine, using only a single field inversion.
- Consolidate precomputation methods into a single one taking a jacobian point and returning an affine table.
- Add secp256k1_ge_mul_lambda method and use in precomputation when endomorphism enabled.