Create private exclusive / single use affine computation slice for an op stmt.

- add util to create a private / exclusive / single use affine
  computation slice for an op stmt (see method doc comment); a single
  multi-result affine_apply op is prepended to the op stmt to provide all
  results needed for its operands as a function of loop iterators and symbols.
- use it for DMA pipelining (to create private slices for DMA start stmt's);
  resolve TODOs/feature request (b/117159533)
- move createComposedAffineApplyOp to Transforms/Utils; free it from taking a
  memref as input / generalize it.

PiperOrigin-RevId: 216926818