This adds an implementation of the ChaCha20Poly1305 AEAD exactly matching
the version specified in RFC8439 section 2.8, including tests and official
test vectors.
This is a partial backport of core#28008
https://github.com/bitcoin/bitcoin/pull/28008/commits/9ff0768bdcca06836ccc673eacfa648e801930cb
Depends on D19017