Please read contributing guidelines. Thanks.

Is your feature request related to a problem? Please describe.
It is thought that stream ciphers are unsafe for shadowsocks. However, XChaCha20-Poly1305-IETF is an AEAD construction, not just a stream cipher.
There is no clear evidence that AEAD constructions with stream ciphers are not safe. And stream ciphers are usually quicker than block ciphers. Furthermore, XChaCha20-Poly1305-IETF is the officially recommended cipher in libsodium documentation. read this

Describe the solution you'd like
Restoring the "XChaCha20-Poly1305-IETF" encryption scheme

Describe alternatives you've considered
None.

Additional context
None.