crypto: require key on ChaCha20 initialization

Summary:
This is a partial backport of core#28100
https://github.com/bitcoin/bitcoin/pull/28100/commits/7d1cd932342e74421ae927800eeada14f504b944
Depends on D19035

Test Plan: ninja all check bitcoin-fuzzers

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D19036