[MLIR][DataLayout] Add support for scalable vectors (#89349)

This commit extends the data layout to support scalable vectors. For
scalable vectors, the `TypeSize`'s scalable field is set accordingly,
and the alignment information remains the same as for normal vectors.
This behavior is in sync with what LLVM's data layout queries are
producing.

Before this change, scalable vectors incorrectly returned the same size
as "normal" vectors.