LayerSet.rename_layer does not set new path

[madig]

A new path should be generated when renaming layers, just like for glyphs.

[cmyr]

yep, sounds like a bug to me.

[madig]

Test cases:

    #[test]
    fn rename_layer() {
        let mut layer_set = LayerSet::default();

        // Non-default layers can be renamed and get a new path.
        layer_set.new_layer("aaa").unwrap();
        assert_eq!(layer_set.get("aaa").unwrap().path().as_os_str(), "glyphs.aaa");

        layer_set.rename_layer("aaa", "bbb", false).unwrap();
        assert_eq!(layer_set.get("bbb").unwrap().path().as_os_str(), "glyphs.bbb");
    }

    #[test]
    fn rename_default_layer() {
        let mut layer_set = LayerSet::default();

        // The default layer can be renamed but the path stays the same.
        layer_set.rename_layer("public.default", "aaa", false).unwrap();

        assert_eq!(*layer_set.default_layer().name(), "aaa");
        assert_eq!(layer_set.default_layer().path().as_os_str(), "glyphs");
    }