In g_irepository_get_object_gtype_interfaces(), returning the address of
the first GIBaseInfo* does not work reliably, because the GIBaseInfos
are not necessarily stored contiguously. So the second and subsequent
ones might be garbage.

Instead, return the address of the array of GIBaseInfo pointers.

Add a test that verifies the functionality, as well.

This is unfortunately an API and ABI break.