Fix coordinate conversion for Unstructured ocr_only partitioning strategy

[bsowell]

There are some quirks with the ocr_only partitioning strategy in unstructured. The expectation in general is that bounding box coordinates are reported counter-clockwise starting at the top-left corner. Since the y-axis increases going down, this means that the second and third points should have higher y-values than the first and last points. This was true for the fast partitioning strategy, but does not appear to always be the case for ocr_only. For example, this are coordinates reported in one case:

{
  "layout_height": 1500,
  "layout_width": 2667,
  "points": [
    [173.0, 1337.0],
    [173.0, 1182.0],
    [2548.0, 1182.0],
    [2548.0, 1337.0]
  ],
  "system": "PixelSpace"
}

You can see here that the points are reported starting at the lower left, and going clockwise. The OCR code in unstructured appears to be undergoing a fairly significant refactoring, so this may be actively changing, but in the meantime, we should make our bounding box conversion behave correctly in this case.

[bsowell]

This was independently reported in the unstructured repo at Unstructured-IO/unstructured#1792