[PowerPC][NFC] Add additional vector_shuffle tests involving scalar_to_vector.

This patch adds additional test cases involving vector_shuffles where either its
left, right or both inputs are scalar_to_vector nodes. These test cases involve
v16i8, v2i64, v4i32 and v8i16 vector shuffles, and were generated in preparation
for D130487.

Differential Revision: https://reviews.llvm.org/D130485