improve import uri completion
currently the ctrl+space completion fails to propose many abs files
1/ it seems to fail to retrieve abs files when editing abs files in lib plugin (such as official_examples/abs.lib/mini.building.abs.model.lib)
2/ Additionally it doesn't propose files located in plugins (such as core.abs.model.lib
) for this second scenario we need a way to declare that core.abs.model.lib contains abs file (via an extension ?)