graphics/poppler: update to 21.08.0

Release 21.08.0:
        core:
         * Add API to allow addition and modification of outlines into a PDF
         * Use additional samples to test for constant parts of an axial gradient
         * forms: Create fallback fonts for some well known font names
         * Support reading the PDF Version from the Catalog
         * Fix XRef::copy when there are modified objects
         * Take into account that Date string may be in unicode
         * JBIG2Stream: Fix regression in "Do not consider a size-0 to be an error"
         * Replace a local bubble sort implementation by std::sort
         * Fix issues with malformed files

        build system:
         * Better error message when libjpeg is not found
         * Better error messages when libopenjpeg2 is not found

        qt5/qt6:
         * Document that a document has to outlive its pages
         * Make getPdfVersion return a dedicated version object

        glib:
         * mimick TextSelectionDumper logic change for spaceAfter

Exp-run by:	antoine
PR:		257539