[mlir][linalg][transform][python] Improve mix-in for PadOp.

In particular:

* Fix and extend the support for constructing possibly nested ArrayAttrs
  from lists of Python ints. This can probably be generalized further
  and used in many more places.
* Add arguments for `pad_to_multiple_of` and `copy_back_op`.
* Format with black and reorder (keyword-only) arguments to match
  tablegen and (`*_gen.py`) order.
* Extend tests for new features.

Reviewed By: springerm

Differential Revision: https://reviews.llvm.org/D157789