This is a backport of secp256k1#1394, secp256k1#1404 and secp256k1#1759
The reduced testing matrix is from https://github.com/bitcoin-core/secp256k1/pull/1313/changes/e9e96482196da641733a8a6763341a84f8b9806a
The CPPFLAGS=-DVERIFY is from https://github.com/bitcoin-core/secp256k1/pull/1172/changes/7f49aa7f2dca595ac8b58d0268dc46a9dfff1e38
Checkout version bumped from 3 to 5:
https://github.com/bitcoin-core/secp256k1/pull/1413/changes/f9b38894baee6b726217e28a4d4591ffdf233e47
https://github.com/bitcoin-core/secp256k1/commit/a889cd93dfe5558aaa0320e241555bb96483c92b
Depends on D19515