Replace smalot/pdfparser with prinsfrank/pdfparser

Switch the PDF extractor from the cosmocode/pdfparser memory fork
(an LGPL smalot/pdfparser fork) to prinsfrank/pdfparser (MIT, built
from scratch,

Replace smalot/pdfparser with prinsfrank/pdfparser

Switch the PDF extractor from the cosmocode/pdfparser memory fork
(an LGPL smalot/pdfparser fork) to prinsfrank/pdfparser (MIT, built
from scratch, zero PHP dependencies beyond prinsfrank/glyph-lists).

PdfExtractor now calls parseFile($path)->getText() in the default
in-memory mode, which benchmarked both faster and far lighter than the
old fork (on a 12 MB/92-page file: 63s/49.5MB vs 68s/100MB), so the
previous setRetainImageContent() tuning is no longer needed.

Known limitation: prinsfrank/pdfparser <= v3.1.0 does not extract text
inside Form XObjects (page content painted with the Do operator, common
in Quartz/Firefox/Chrome PDFs such as the Tika sample), so
PdfExtractorTest::testExtractsText fails against stock v3.1.0.

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