properties: add "Contains javascript" document property
and implement it for poppler backend. This property
tells the user if the pdf has any javascript in it,
it's shown in the document properties dialog.
This depends on the new poppler-glib api:
gboolean poppler_document_has_javascript (PopplerDocument *document);
which is being proposed in:
https://gitlab.freedesktop.org/poppler/poppler/-/merge_requests/571