ManPageDocumentation: expand unsupported links on pages
file:// URL links don't work in Qt WebEngine because it forbids such file system access. help:/ links don't work because the KDE help URL scheme is not registered with Qt WebKit or Qt WebEngine. Currently the HTML of each man page contains two stylesheet links with the following URLs: file:///usr/share/kio_docfilter/kio_docfilter.css help:/kdoctools5-common/kde-default.css The kio_docfilter style sheet forces white background color, affects the appearance of #header (the top banner that is hidden by manpagedocumentation.css) and #footer (nicely separates the bottom "Generated by kio_man version 22.04.2" text from the man page itself). The kde-default.css affects many elements of a man page. Whether the page looks better as a result is subjective. But at least it works as intended and is consistent with KHelpCenter's rendering.