The source project of this merge request has been removed.
docs: Switch to gi-docgen
- Don't build docs in flatpak. It would require a bunch of extra modules for gi-docgen's dependencies, and doc generation can take a little while anyway. Better to leave it out.
- Remove the gtk-doc files and add gi-docgen to the build system.
- Convert the docs to the new format.
- Update up some of the docs here and there.