glib: Rearrange layout for annotations in demo

Add render area to visualize the annotations per page.
glib: Expand short names for annotations
glib: Auto-update annotation list and render page in demo
glib: Add attempt to support line annotations
glib: Add demo for line annotations
glib: Add demo for simple line annotations
glib: Aggregate showing individuals widgets as one single show_all
glib: Add PopplerQuadrilateral boxed type
glib: Add PopplerAnnotTextMarkup object

Signed-off-by: Germán Poo-Caamaño <gpoo@gnome.org>
glib: Add support for PopplerTextAnnotMarkup to the demo.
glib: Add PopplerAnnotTextHighlight object

Signed-off-by: Germán Poo-Caamaño <gpoo@gnome.org>
glib: Add PopplerAnnotTextUnderline object

Signed-off-by: Germán Poo-Caamaño <gpoo@gnome.org>
glib: Add PopplerAnnotTextSquiggly object

Signed-off-by: Germán Poo-Caamaño <gpoo@gnome.org>
glib: Add PopplerAnnotTextStrikeOut object

Signed-off-by: Germán Poo-Caamaño <gpoo@gnome.org>
glib: Add references in poppler-sections

Signed-off-by: Germán Poo-Caamaño <gpoo@gnome.org>
glib: Add save to file in demo

Useful to save PDF with annotations and compare the resulting file
later.