* Add failing test for decoding ShortU16 alias values (cherry picked from commit338f66f9aa) * Factor out ShortU16 deser vistor logic to helper (cherry picked from commit6222fbcc66) * Reimplement decode_len() with ShortU16 vistor helper (cherry picked from commit30dbe257cf) Co-authored-by: Trent Nelson <trent@solana.com>