gi/types: make it possible to resolve ambiguous vmethod names
gi/types: make it possible to resolve ambiguous vmethod names

Related to https://gitlab.gnome.org/GNOME/pygobject/issues/105,
but the method exposed to resolve the ambiguities does not
use a decorator, as a decorator cannot rename the function it
wraps, which means that users will have to provide different names
if they want to implement ambiguous methods from multiple base
classes.

Instead, ambiguities can be resolved by implementing methods named
do_$namespaced_base_class_name_$vfunc_name, eg:

do_gst_base_src_query

GNOME/pygobject,GNOME/pygobject,pexip/pygobject,pexip/pygobject,pexip/pygobject,GNOME/pygobject