LibWeb: Move timer implementations to WindowOrWorkerGlobalScopeMixin

This is where it belongs according to the spec, and where these methods'
IDL will be placed.

This forces us to implement a few steps closer to the spec as well.

Userland/Libraries/LibWeb/HTML/WorkerGlobalScope.cpp

@@ -37,6 +37,8 @@ JS::ThrowCompletionOr<void> WorkerGlobalScope::initialize(JS::Realm& realm)
 void WorkerGlobalScope::visit_edges(Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);
+    WindowOrWorkerGlobalScopeMixin::visit_edges(visitor);
+
     visitor.visit(m_location.ptr());
     visitor.visit(m_navigator.ptr());
 }