Reland D143267: [LoopVectorize] Use DataLayout::getIndexType instead of i32...

Reland D143267: [LoopVectorize] Use DataLayout::getIndexType instead of i32 for non-constant GEP indices.

Fixed issue where 'ConstantInt::get(IndextTy, -Part)' was executed with the wrong type for Part,
e.g. IndexTy was i64, but Part was 'unsigned', which led to things like 'mul i64 .., 4294967292',
which was obviously wrong.

Also changed sve-vector-reverse.ll to be vectorized with UF>1 to test this.

This reverts commit 1f01cdda.