[Python API] Fix opset16 missing opset15 re-exports (#34782)
`openvino.opset16` was missing 10 re-exports of ops introduced in
opset15. Since OpenVINO opsets are cumulative, all opset15 ops must be
accessible via opset16.
Ops missing:
- col2im
- embedding_bag_offsets
- embedding_bag_packed
- scatter_nd_update
- roi_align_rotated
- string_tensor_pack
- string_tensor_unpack
- bitwise_left_shift
- bitwise_right_shift
- slice_scatter
Also moved `search_sorted`, `squeeze`, and `stft` from the previous
opsets section to the new operations section where they belong for
opset15.
Closes: #34780
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