Implement sa_decode with ARM SIMD (NEON) (#2390)

Summary:
This PR implements `faiss/cppcontrib/SaDecodeKernels-neon-inl.h` based from `faiss/cppcontrib/SaDecodeKernels-neon-avx2.h` .

Pull Request resolved: #2390

Reviewed By: mdouze

Differential Revision: D38009788

Pulled By: alexanderguzhva

fbshipit-source-id: 666436f8eec82b31507f379e3f136b73804a1870

Author: wx257osn2