[VectorCombine] Don't vectorize scalar load under asan/hwasan/memtag/tsan

Similar to the tsan suppression in
`Utils/VNCoercion.cpp:getLoadLoadClobberFullWidthSize` (rL175034; load widening used by GVN),
the D81766 optimization should be suppressed under tsan due to potential
spurious data race reports:

  struct A {
    int i;
    const short s; // the load cannot be vectorized because
    int modify;    // it overlaps with bytes being concurrently modified
    long pad1, pad2;
  };
  // __tsan_read16 does not know that some bytes are undef and accessing is safe

Similarly, under asan, users can mark memory regions with
`__asan_poison_memory_region`. A widened load can lead to a spurious
use-after-poison error. hwasan/memtag should be similarly suppressed.

`mustSuppressSpeculation` suppresses asan/hwasan/tsan but not memtag, so
we need to exclude memtag in `vectorizeLoadInsert`.

Note, memtag suppression can be relaxed if the load is aligned to the
its granule (usually 16), but that is out of scope of th...