feat: `partiton_pdf()` set inferred elements text (#3061)
This PR adds the ability to fill inferred elements text from embedded
text (`pdfminer`) without depending on `unstructured-inference` library.
This PR is the second part of moving embedded text related code from
`unstructured-inference` to `unstructured` and works together with
https://github.com/Unstructured-IO/unstructured-inference/pull/349.
