[AArch64] Add tests for dotreduce to check for wider vectors.

Currently we only reduce vector.reduce.add to sdot if the vectors are either <8 x i8> or <16 x i8>.

Reviewed By: fhahn

Differential Revision: https://reviews.llvm.org/D141692

(cherry-picked from 32d72bd)

Author: Zain Jaffal