[NFC] Add tests for scalable vectorization of loops with large stride acesses

This patch just adds tests that we can vectorize loop such as these:

  for (i = 0; i < n; i++)
    dst[i * 7] += 1;

and

  for (i = 0; i < n; i++)
    if (cond[i])
      dst[i * 7] += 1;

using scalable vectors, where we expect to use gathers and scatters in the
vectorized loop. The vector of pointers used for the gather is identical
to those used for the scatter so there should be no memory dependences.

Tests are added here:

  Transforms/LoopVectorize/AArch64/sve-large-strides.ll

Differential Revision: https://reviews.llvm.org/D99192