Fix window double borrows (#23739)

Fix bugs caused by the window context PR, where the window could be on
the stack and is then requested from the App.
This PR also adds derive macros for `AppContext` and `VisualContext` so
that it's easy to define further contexts in API code, such as
`editor::BlockContext`.

Release Notes:

- N/A

crates/editor/src/display_map/block_map.rs

@@ -225,8 +225,11 @@ pub enum BlockStyle {
     Sticky,
 }
 
+#[derive(gpui::AppContext, gpui::VisualContext)]
 pub struct BlockContext<'a, 'b> {
+    #[window]
     pub window: &'a mut Window,
+    #[app]
     pub app: &'b mut App,
     pub anchor_x: Pixels,
     pub max_width: Pixels,