Add SECP256K1_FE_STORAGE_CONST_GET to 5x52 field
Add SECP256K1_FE_STORAGE_CONST_GET to 5x52 field

So far this has not been needed, as it's only used by the static precomputation
which always builds with 32-bit fields.

This prepares for the ability to have __int128 detected on the C side, breaking
that restriction.

bitcoin/secp256k1,afk11/secp256k1,bitcoin/secp256k1,ElementsProject/secp256k1-zkp,bitcoin-core/secp256k1,afk11/secp256k1,ElementsProject/secp256k1-zkp,afk11/secp256k1,evoskuil/secp256k1,peterdettman/secp256k1,afk11/secp256k1,evoskuil/secp256k1,evoskuil/secp256k1,bitcoin/secp256k1,bitcoin-core/secp256k1,afk11/secp256k1,peterdettman/secp256k1,evoskuil/secp256k1,bitcoin/secp256k1,bitcoin/secp256k1,evoskuil/secp256k1