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_demo_app/src/accessibility_inspector.rs

@@ -5,11 +5,11 @@ use accesskit_consumer::{FilterResult, Node, Tree, TreeChangeHandler};
 
 use eframe::epaint::text::TextWrapMode;
 use egui::{
-    Button, Color32, Context, Event, Frame, FullOutput, Id, Key, KeyboardShortcut, Label,
-    Modifiers, Panel, RawInput, RichText, ScrollArea, Ui, collapsing_header::CollapsingState,
+    Button, Color32, Event, Frame, FullOutput, Id, Key, KeyboardShortcut, Label, Modifiers, Panel,
+    RawInput, RichText, ScrollArea, Ui, collapsing_header::CollapsingState,
 };
 
-/// This [`egui::Plugin`] adds an inspector Panel.
+/// This [`egui::Plugin`] adds an inspector panel.
 ///
 /// It can be opened with the `(Cmd/Ctrl)+Alt+I`. It shows the current AccessKit tree and details
 /// for the selected node.
@@ -71,8 +71,8 @@ impl egui::Plugin for AccessibilityInspectorPlugin {
         }
     }
 
-    fn on_begin_pass(&mut self, ctx: &Context) {
-        if ctx.input_mut(|i| {
+    fn on_begin_pass(&mut self, ui: &mut Ui) {
+        if ui.input_mut(|i| {
             i.consume_shortcut(&KeyboardShortcut::new(
                 Modifiers::COMMAND | Modifiers::ALT,
                 Key::I,
@@ -85,9 +85,9 @@ impl egui::Plugin for AccessibilityInspectorPlugin {
             return;
         }
 
-        ctx.enable_accesskit();
+        ui.enable_accesskit();
 
-        Panel::right(Self::id()).show(ctx, |ui| {
+        Panel::right(Self::id()).show_inside(ui, |ui| {
             ui.heading("🔎 AccessKit Inspector");
             if let Some(selected_node) = self.selected_node {
                 Panel::bottom(Self::id().with("details_panel"))

crates/egui_demo_app/src/wrap_app.rs

@@ -271,7 +271,7 @@ impl eframe::App for WrapApp {
         color.to_normalized_gamma_f32()
     }
 
-    fn update(&mut self, ctx: &egui::Context, frame: &mut eframe::Frame) {
+    fn ui(&mut self, ui: &mut egui::Ui, frame: &mut eframe::Frame) {
         #[cfg(target_arch = "wasm32")]
         if let Some(anchor) = frame
             .info()
@@ -285,36 +285,36 @@ impl eframe::App for WrapApp {
         }
 
         #[cfg(not(target_arch = "wasm32"))]
-        if ctx.input_mut(|i| i.consume_key(egui::Modifiers::NONE, egui::Key::F11)) {
-            let fullscreen = ctx.input(|i| i.viewport().fullscreen.unwrap_or(false));
-            ctx.send_viewport_cmd(egui::ViewportCommand::Fullscreen(!fullscreen));
+        if ui.input_mut(|i| i.consume_key(egui::Modifiers::NONE, egui::Key::F11)) {
+            let fullscreen = ui.input(|i| i.viewport().fullscreen.unwrap_or(false));
+            ui.send_viewport_cmd(egui::ViewportCommand::Fullscreen(!fullscreen));
         }
 
         let mut cmd = Command::Nothing;
         egui::Panel::top("wrap_app_top_bar")
             .frame(egui::Frame::new().inner_margin(4))
-            .show(ctx, |ui| {
+            .show_inside(ui, |ui| {
                 ui.horizontal_wrapped(|ui| {
                     ui.visuals_mut().button_frame = false;
                     self.bar_contents(ui, frame, &mut cmd);
                 });
             });
 
-        self.state.backend_panel.update(ctx, frame);
+        self.state.backend_panel.update(ui.ctx(), frame);
 
-        egui::CentralPanel::no_frame().show(ctx, |ui| {
-            if !is_mobile(ctx) {
+        egui::CentralPanel::no_frame().show_inside(ui, |ui| {
+            if !is_mobile(ui.ctx()) {
                 cmd = self.backend_panel(ui, frame);
             }
 
             self.show_selected_app(ui, frame);
         });
 
-        self.state.backend_panel.end_of_frame(ctx);
+        self.state.backend_panel.end_of_frame(ui.ctx());
 
-        self.ui_file_drag_and_drop(ctx);
+        self.ui_file_drag_and_drop(ui.ctx());
 
-        self.run_cmd(ctx, cmd);
+        self.run_cmd(ui.ctx(), cmd);
     }
 
     #[cfg(feature = "glow")]