auto strategy was choosing the fast strategy in cases where the pdf contents were just a flat image, resulting in no output. This PR changes the behavior of auto so that elements that can be extracted by fast are extracted, a cursory examination of the elements is made to see if there are elements with text present, and if so then these elements are used as the output. Otherwise fallback strategies come into play.
Summary
* Updates "fast" PDF output element ordering to be consistent across Python versions by using the X,Y coordinates of elements extracted
* Added PDFs ingest tests with fast strategy with new script ./test_unstructured_ingest/test-ingest-pdf-fast-reprocess.sh
Updated ingest tests procedure:
* Processing files with hi_res strategy, and preserve downloads to repo files-ingest-download/<ingest_test_name>
* Reprocessing all PDFs with fast strategy from local file files-ingest-download, the partition outputs are stored at expected-structured-output/pdf-fast-reprocess/<ingest_test_name>
Test
* Reproduce tests with ./scripts/ingest-test-fixtures-update.sh , should expect no update. Also don't need any secret tokens since relevant tests won't produce PDFs.
