Eliminate GPUI View, ViewContext, and WindowContext types (#22632)

There's still a bit more work to do on this, but this PR is compiling
(with warnings) after eliminating the key types. When the tasks below
are complete, this will be the new narrative for GPUI:

- `Entity<T>` - This replaces `View<T>`/`Model<T>`. It represents a unit
of state, and if `T` implements `Render`, then `Entity<T>` implements
`Element`.
- `&mut App` This replaces `AppContext` and represents the app.
- `&mut Context<T>` This replaces `ModelContext` and derefs to `App`. It
is provided by the framework when updating an entity.
- `&mut Window` Broken out of `&mut WindowContext` which no longer
exists. Every method that once took `&mut WindowContext` now takes `&mut
Window, &mut App` and every method that took `&mut ViewContext<T>` now
takes `&mut Window, &mut Context<T>`

Not pictured here are the two other failed attempts. It's been quite a
month!

Tasks:

- [x] Remove `View`, `ViewContext`, `WindowContext` and thread through
`Window`
- [x] [@cole-miller @mikayla-maki] Redraw window when entities change
- [x] [@cole-miller @mikayla-maki] Get examples and Zed running
- [x] [@cole-miller @mikayla-maki] Fix Zed rendering
- [x] [@mikayla-maki] Fix todo! macros and comments
- [x] Fix a bug where the editor would not be redrawn because of view
caching
- [x] remove publicness window.notify() and replace with
`AppContext::notify`
- [x] remove `observe_new_window_models`, replace with
`observe_new_models` with an optional window
- [x] Fix a bug where the project panel would not be redrawn because of
the wrong refresh() call being used
- [x] Fix the tests
- [x] Fix warnings by eliminating `Window` params or using `_`
- [x] Fix conflicts
- [x] Simplify generic code where possible
- [x] Rename types
- [ ] Update docs

### issues post merge

- [x] Issues switching between normal and insert mode
- [x] Assistant re-rendering failure
- [x] Vim test failures
- [x] Mac build issue



Release Notes:

- N/A

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Cole Miller <cole@zed.dev>
Co-authored-by: Mikayla <mikayla@zed.dev>
Co-authored-by: Joseph <joseph@zed.dev>
Co-authored-by: max <max@zed.dev>
Co-authored-by: Michael Sloan <michael@zed.dev>
Co-authored-by: Mikayla Maki <mikaylamaki@Mikaylas-MacBook-Pro.local>
Co-authored-by: Mikayla <mikayla.c.maki@gmail.com>
Co-authored-by: joão <joao@zed.dev>

crates/markdown/examples/markdown.rs

@@ -1,5 +1,5 @@
 use assets::Assets;
-use gpui::{prelude::*, rgb, App, KeyBinding, StyleRefinement, View, WindowOptions};
+use gpui::{prelude::*, rgb, Application, Entity, KeyBinding, StyleRefinement, WindowOptions};
 use language::{language_settings::AllLanguageSettings, LanguageRegistry};
 use markdown::{Markdown, MarkdownStyle};
 use node_runtime::NodeRuntime;
@@ -7,7 +7,7 @@ use settings::SettingsStore;
 use std::sync::Arc;
 use theme::LoadThemes;
 use ui::prelude::*;
-use ui::{div, WindowContext};
+use ui::{div, App, Window};
 
 const MARKDOWN_EXAMPLE: &str = r#"
 # Markdown Example Document
@@ -99,7 +99,7 @@ Remember, markdown processors may have slight differences and extensions, so alw
 
 pub fn main() {
     env_logger::init();
-    App::new().with_assets(Assets).run(|cx| {
+    Application::new().with_assets(Assets).run(|cx| {
         let store = SettingsStore::test(cx);
         cx.set_global(store);
         language::init(cx);
@@ -118,8 +118,8 @@ pub fn main() {
         Assets.load_fonts(cx).unwrap();
 
         cx.activate(true);
-        cx.open_window(WindowOptions::default(), |cx| {
-            cx.new_view(|cx| {
+        cx.open_window(WindowOptions::default(), |window, cx| {
+            cx.new(|cx| {
                 let markdown_style = MarkdownStyle {
                     base_text_style: gpui::TextStyle {
                         font_family: "Zed Plex Sans".into(),
@@ -164,6 +164,7 @@ pub fn main() {
                     MARKDOWN_EXAMPLE.to_string(),
                     markdown_style,
                     language_registry,
+                    window,
                     cx,
                 )
             })
@@ -173,7 +174,7 @@ pub fn main() {
 }
 
 struct MarkdownExample {
-    markdown: View<Markdown>,
+    markdown: Entity<Markdown>,
 }
 
 impl MarkdownExample {
@@ -181,16 +182,17 @@ impl MarkdownExample {
         text: String,
         style: MarkdownStyle,
         language_registry: Arc<LanguageRegistry>,
-        cx: &mut WindowContext,
+        window: &mut Window,
+        cx: &mut App,
     ) -> Self {
         let markdown =
-            cx.new_view(|cx| Markdown::new(text, style, Some(language_registry), None, cx));
+            cx.new(|cx| Markdown::new(text, style, Some(language_registry), None, window, cx));
         Self { markdown }
     }
 }
 
 impl Render for MarkdownExample {
-    fn render(&mut self, _cx: &mut ViewContext<Self>) -> impl IntoElement {
+    fn render(&mut self, _window: &mut Window, _cx: &mut Context<Self>) -> impl IntoElement {
         div()
             .id("markdown-example")
             .debug_selector(|| "foo".into())