WIP: docs: re-enable gtk-doc
From the last commit:
gtk-doc support was removed around 3 years ago with commit 7dc0b0e6. Now that we have Meson and [MRs related to documentation], it makes sense to re-enable this, so people who want to use libmutter can do so without having to actually dive in the code. [MRs related to documentation]: https://gitlab.gnome.org/GNOME/mutter/merge_requests/269
Apart from some small changes to fix some issues, the biggest change is that we need to have another (non-installed) build of mutter without hidden symbols. This to make sure we're not accidentally hiding any
get_type() function which is needed for gtk-doc to introspect the type.
Some stuff still needs to happen of course:
- Decide on the structure of the reference document: how do we make a difference between public/private API?
- We need an option to build the documentation conditionally
- Put a step into the CI to publish on pages.gitlab.gnome.org