eframe: Replace Frame::update with fn logic and fn ui (#7775)

* Part of https://github.com/emilk/egui/issues/5113
* Part of https://github.com/emilk/egui/issues/3524

## What
This deprecates `eframe::App::update` and replaces it with two new
functions:

```rs
pub trait App {
	/// Called just before `ui`, and in the future this will
    /// also be called for background apps when needed.
	fn logic(&mut self, ctx: &egui::Context, frame: &mut Frame) { }
	
    /// Show your user interface to the user.
	fn ui(&mut self, ui: &mut egui::Ui, frame: &mut Frame);

	…
}
```

Similarly, `Context::run` is deprecated in favor of `Context::run_ui`.

`Plugin`s are now handed a `Ui` instead of just a `Context` in
`on_begin/end_frame`.

## TODO
…either in this PR or a later one
* [x] Deprecate `App::update`
* [x] Deprecate `Context::run`
* [x] Change plugins to get a `Ui`
* [x] Update kittest
* [x] Change viewports to get UI:s (`show_viewport_immediate` etc)
  - https://github.com/emilk/egui/pull/7779

## Later PRs
* [ ] Deprecate `Panel::show`
* [ ] Deprecate `CentralPanel::show`
* [ ] Deprecate `CentralPanel` ?

crates/egui_glow/examples/pure_glow.rs

@@ -215,10 +215,11 @@ impl winit::application::ApplicationHandler<UserEvent> for GlowApp {
         let mut redraw = || {
             let mut quit = false;
 
-            self.egui_glow.as_mut().unwrap().run(
-                self.gl_window.as_mut().unwrap().window(),
-                |egui_ctx| {
-                    egui::Panel::left("my_side_panel").show(egui_ctx, |ui| {
+            self.egui_glow
+                .as_mut()
+                .unwrap()
+                .run(self.gl_window.as_mut().unwrap().window(), |ui| {
+                    egui::Panel::left("my_side_panel").show_inside(ui, |ui| {
                         ui.heading("Hello World!");
                         if ui.button("Quit").clicked() {
                             quit = true;
@@ -226,8 +227,7 @@ impl winit::application::ApplicationHandler<UserEvent> for GlowApp {
 
                         ui.color_edit_button_rgb(self.clear_color.as_mut().try_into().unwrap());
                     });
-                },
-            );
+                });
 
             if quit {
                 event_loop.exit();