When a pdf file is opened with pdfium and then saved as odg, each page is saved as a draw:image of the pdf. But since no page number info was given, when opening the odg file, all the pages are shown as the first one. This adds a loext:page-number to the saved odg and the logic to load a specific page from an embedded pdf. Added loadGraphicAtPage to XGraphicStorageHandler. Change-Id: I398b7ad7f03cc7fb930a4e7b7620c6f238b41c0d Reviewed-on: https://gerrit.libreoffice.org/c/core/+/181066 Tested-by: Jenkins Reviewed-by: Miklos Vajna <vmiklos@collabora.com>