Whitespaces in the filenames proposed by the export tools are replaced with + signs

Removing the "Old Core - PDF Export" component since the old PDF export is now deprecated, see https://forum.xwiki.org/t/deprecate-old-pdf-export-and-retire-it/13520. Thus, all issues except blocker issues are going to be moved to the client-side PDF component or closed as won't fix. Ofc, if anyone wants to fix this issue on the old server-side PDF export, they're free to go ahead and we'll add back the old component.