Add fuzz test for testing that ChaCha20 works as a stream

Summary:
This is a partial backport of core#26153
https://github.com/bitcoin/bitcoin/pull/26153/commits/38eaece67b1bc37b2f502348c5d7537480a34346

Depends on D18820

Test Plan: ninja bitcoin-fuzzers

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18821