LibWeb/HTML: Port Window.atob() to IDL

Author: https://github.com/linusg
Commit: 6dd1934ed8
Pull-request: https://github.com/SerenityOS/serenity/pull/17752
Reviewed-by: https://github.com/awesomekling

Userland/Libraries/LibWeb/HTML/Window.h

@@ -46,6 +46,7 @@ public:
 
     ~Window();
 
+    using WindowOrWorkerGlobalScopeMixin::atob;
     using WindowOrWorkerGlobalScopeMixin::btoa;
 
     // ^DOM::EventTarget
@@ -266,7 +267,6 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(clear_timeout);
     JS_DECLARE_NATIVE_FUNCTION(request_animation_frame);
     JS_DECLARE_NATIVE_FUNCTION(cancel_animation_frame);
-    JS_DECLARE_NATIVE_FUNCTION(atob);
     JS_DECLARE_NATIVE_FUNCTION(focus);
 
     JS_DECLARE_NATIVE_FUNCTION(get_computed_style);