LibWeb: Implement BarProp properties for Window

Author: https://github.com/Totto16
Commit: b66e7ac1ba
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3810
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/tcl3 ✅

Libraries/LibWeb/HTML/BarProp.idl

@@ -0,0 +1,6 @@
+
+// https://html.spec.whatwg.org/multipage/nav-history-apis.html#barprop
+[Exposed=Window]
+interface BarProp {
+    readonly attribute boolean visible;
+};