Change exhaustive test groups so they have a point with X=1

Summary:
This enables testing overflow is correctly encoded in the recid, and
likely triggers more edge cases.

Also introduce a Sage script to generate the parameters.

This is a partial backport of secp256k1 PR808 : https://github.com/bitcoin-core/secp256k1/pull/808/commits/b110c106fa9704e30f6b0c2ffa6a2697031e89a8

Depends on D7659

Test Plan:

ninja check-secp256k1

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D7660