How can style_ui be used in a post-Context era?

[mkeeter]

Context::style_ui takes a &mut ui. In a post-0.3.4 world where Context is accessed through deref on Ui, this runs afoul of the borrow checker:

egui::Window::new("Debug").show(ui, |ui| {
     ui.style_ui(ui, egui::Theme::Light) // can't borrow ui while calling style_ui!
});

Should style_ui be moved to live in Ui instead, to be invoked with ui.style_ui(egui::Theme::Light)? I'd be happy to do a PR if that seems reasonable.