[SECP256K1] Improve field/scalar inverse tests
Summary:
Add a new run_inverse_tests that replaces all existing field/scalar inverse tests, and tests a few identities for fixed inputs, small numbers (-999...999), random inputs (structured and unstructured), as well as comparing with the output of secp256k1_fe_inv_all_var.
Partial backport of secp256k1#831:
https://github.com/bitcoin-core/secp256k1/pull/831/commits/aa9cc5218001f14f4312bde1058417d4b755fd11
Depends on D9405.
Test Plan:
ninja check-secp256k1
Reviewers: #bitcoin_abc, majcosta
Reviewed By: #bitcoin_abc, majcosta
Differential Revision: https://reviews.bitcoinabc.org/D9406