When generating introspection data, we instantiate types without
calling gtk_init, so make sure that extension points are registered
before the type is trying to implement them.
Add an extension point called gtk-im-module, which requires
the type GtkIMContext. Simplify the loading by using GIO
infrastructure. Drop the locale filtering for now, I don't
think it is really necessary nowadays.
Convert existing platform modules to gio modules.
Sill to do: Drop the conditional build machinery.
Either always include them, or never.
Move the remaining struct definition into gtkimcontextinfo.h and include
that header in gtk.h. gtkimmodule.h is now an empty header. We should
probably deprecate it somehow.
This is also necessary so headers used in gtk .c files don't include
gtk.h which in turn includes all the deprecated headers which we want to
avoid so we can include them with deprecation warnings turned off.
