Recommend that scope implementations should fall
back to or derive from GtkBuilderCScope in order
to not lose GTK's type-guessing machinery.
Related: #5398
Remove a boatload of "or %NULL" from nullable parameters
and return values. gi-docgen generates suitable text from
the annotation that we don't need to duplicate.
This adds a few missing nullable annotations too.
When looking for the get_type function for GThemedIcon,
try both g_themed_icon_get_type and gthemed_icon_get_type
The former is what gio has, the latter is still supported
to avoid breaking gweather_location_get_type.
Update tests to cover this new case.
GtkBuilderScope is an interface that provides the scope that a builder
instance operates in.
It creates closures and resolves types. Language bindings are meant to
use this interface to customize the behavior of builder files, in
particular when instantiating templates.
A default implementation for C is provided via GtkBuilderCScope (to keep
with the awkward naming that glib uses for closures). It is derivable on
purpose so that languages or extensions that extend C can use it.
The reftest code in fact does derive GtkBuilderCScope for its own scope
implementation that implements looking up symbols in modules.
gtk-widget-factory was updated to use the new GtkBuilderCScope to add
its custom callback symbols.
So it does it different from gtk-demo, which uses the normal way of
exporting symbols for dlsym() and thereby makes the 2 demos test the 2
ways GtkBuilder uses for looking up symbols.
