GdkContentFormatsBuilder is currently not introspectable, as it does not
have a GType. We can turn it into a boxed type, but we need to implement
memory management for it.
The current gdk_content_formats_builder_free() function returns a newly
constructed value, so we cannot use it as a GBoxedFreeFunc; additionally
copying a GdkContentFormatsBuilder contents would make it a bit odd, as
you could get multiple identical GdkContentFormats out of the copies.
A simple approach is to model the GdkContentFormatsBuilder API to follow
the GBytes one: use reference counting for memory management, and have
a function to release a reference, return a GdkContentFormats, and reset
the GdkContentFormatsBuilder state.
For language bindings, we can provide a get_formats() function that
returns the GdkContentFormats instance and resets the builder instance,
leaving the reference count untouched.
For C convenience we can keep gdk_content_formats_builder_free(), and
make it a wrapper around gdk_content_formats_builder_get_formats(), with
the guarantee that it'll free the builder instance regardless of its
current reference count.
https://bugzilla.gnome.org/show_bug.cgi?id=793097https://blogs.gnome.org/otte/2018/02/03/builders/
As far as possible, use per-display debug flags.
This will minimize the debug spew that we get from
the inspector if it is running on a separate display.
I decided to put this in a custom subclass, because then I could keep
the whole gtk primary protocol self-contained.
The other option would have been reusing GdkWaylandClipboard, but that
didn't seem worth it, especially because that code needs to interact
with the DND machinery, while the primary doesn't.
