A loaded #PeasPluginInfo.
The implemented extension #GType.
the name of the first property.
the value of the first property, followed optionally by more name/value pairs, followed by %NULL.
a new instance of #PeasExtension wrapping the @extension_type instance, or %NULL.
If the plugin identified by @info implements the @extension_type, then this function will return a new instance of this implementation, wrapped in a new #PeasExtension instance. Otherwise, it will return %NULL.
Since libpeas 1.22, @extension_type can be an Abstract #GType and not just an Interface #GType.
See peas_engine_create_extension() for more information.