[mlir][Linalg] Add a transform.structured.lower_pack op

This revision introduces `transform.structured.lower_pack` which allows
rewriting a `tensor.pack` to `tensor.pad` + `tensor.expand_shape` + `linalg.transpose`.

The implementation is currently limited to static pack ops that do not have outer_dims permutations.

Differential Revision: https://reviews.llvm.org/D142881