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/feature_flags/src/feature_flags.rs

@@ -1,10 +1,6 @@
 use futures::{channel::oneshot, FutureExt as _};
-use gpui::{AppContext, Global, Subscription, ViewContext};
-use std::{
-    future::Future,
-    pin::Pin,
-    task::{Context, Poll},
-};
+use gpui::{App, Context, Global, Subscription, Window};
+use std::{future::Future, pin::Pin, task::Poll};
 
 #[derive(Default)]
 struct FeatureFlags {
@@ -101,22 +97,22 @@ impl FeatureFlag for AutoCommand {
 }
 
 pub trait FeatureFlagViewExt<V: 'static> {
-    fn observe_flag<T: FeatureFlag, F>(&mut self, callback: F) -> Subscription
+    fn observe_flag<T: FeatureFlag, F>(&mut self, window: &Window, callback: F) -> Subscription
     where
-        F: Fn(bool, &mut V, &mut ViewContext<V>) + Send + Sync + 'static;
+        F: Fn(bool, &mut V, &mut Window, &mut Context<V>) + Send + Sync + 'static;
 }
 
-impl<V> FeatureFlagViewExt<V> for ViewContext<'_, V>
+impl<V> FeatureFlagViewExt<V> for Context<'_, V>
 where
     V: 'static,
 {
-    fn observe_flag<T: FeatureFlag, F>(&mut self, callback: F) -> Subscription
+    fn observe_flag<T: FeatureFlag, F>(&mut self, window: &Window, callback: F) -> Subscription
     where
-        F: Fn(bool, &mut V, &mut ViewContext<V>) + 'static,
+        F: Fn(bool, &mut V, &mut Window, &mut Context<V>) + 'static,
     {
-        self.observe_global::<FeatureFlags>(move |v, cx| {
+        self.observe_global_in::<FeatureFlags>(window, move |v, window, cx| {
             let feature_flags = cx.global::<FeatureFlags>();
-            callback(feature_flags.has_flag::<T>(), v, cx);
+            callback(feature_flags.has_flag::<T>(), v, window, cx);
         })
     }
 }
@@ -130,10 +126,10 @@ pub trait FeatureFlagAppExt {
 
     fn observe_flag<T: FeatureFlag, F>(&mut self, callback: F) -> Subscription
     where
-        F: FnMut(bool, &mut AppContext) + 'static;
+        F: FnMut(bool, &mut App) + 'static;
 }
 
-impl FeatureFlagAppExt for AppContext {
+impl FeatureFlagAppExt for App {
     fn update_flags(&mut self, staff: bool, flags: Vec<String>) {
         let feature_flags = self.default_global::<FeatureFlags>();
         feature_flags.staff = staff;
@@ -159,7 +155,7 @@ impl FeatureFlagAppExt for AppContext {
 
     fn observe_flag<T: FeatureFlag, F>(&mut self, mut callback: F) -> Subscription
     where
-        F: FnMut(bool, &mut AppContext) + 'static,
+        F: FnMut(bool, &mut App) + 'static,
     {
         self.observe_global::<FeatureFlags>(move |cx| {
             let feature_flags = cx.global::<FeatureFlags>();
@@ -196,7 +192,7 @@ pub struct WaitForFlag(oneshot::Receiver<bool>, Option<Subscription>);
 impl Future for WaitForFlag {
     type Output = bool;
 
-    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+    fn poll(mut self: Pin<&mut Self>, cx: &mut core::task::Context<'_>) -> Poll<Self::Output> {
         self.0.poll_unpin(cx).map(|result| {
             self.1.take();
             result.unwrap_or(false)