collab ui: Fix notification windows on external monitors (#9817)

Sharing a project displays a notification (window) on every screen.
Previously there was an issue with the positioning of windows on all
screens except the primary screen.

As you can see here:


![image](https://github.com/zed-industries/zed/assets/53836821/314cf367-8c70-4e8e-bc4a-dcbb99cb4f71)

Now:


![image](https://github.com/zed-industries/zed/assets/53836821/42af9ef3-8af9-453a-ad95-147b5f9d90ba)

@mikayla-maki and I also decided to refactor the `WindowOptions` a bit. 
Previously you could specify bounds which controlled the positioning and
size of the window in the global coordinate space, while also providing
a display id (which screen to show the window on). This can lead to
unusual behavior because you could theoretically specify a global bound
which does not even belong to the display id which was provided.

Therefore we changed the api to this:
```rust
struct WindowOptions {
    /// The bounds of the window in screen coordinates
    /// None -> inherit, Some(bounds) -> set bounds.
    pub bounds: Option<Bounds<DevicePixels>>,

    /// The display to create the window on, if this is None,
    /// the window will be created on the main display
    pub display_id: Option<DisplayId>,
}
```

This lets you specify a display id, which maps to the screen where the
window should be created and bounds relative to the upper left of the
screen.

Release Notes:

- Fixed positioning of popup windows (e.g. when sharing a project) when
using multiple external displays.

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/gpui/src/app.rs

@@ -30,11 +30,11 @@ use util::{
 use crate::{
     current_platform, image_cache::ImageCache, init_app_menus, Action, ActionRegistry, Any,
     AnyView, AnyWindowHandle, AppMetadata, AssetSource, BackgroundExecutor, ClipboardItem, Context,
-    DispatchPhase, Entity, EventEmitter, ForegroundExecutor, Global, KeyBinding, Keymap, Keystroke,
-    LayoutId, Menu, PathPromptOptions, Pixels, Platform, PlatformDisplay, Point, PromptBuilder,
-    PromptHandle, PromptLevel, Render, RenderablePromptHandle, SharedString, SubscriberSet,
-    Subscription, SvgRenderer, Task, TextSystem, View, ViewContext, Window, WindowAppearance,
-    WindowContext, WindowHandle, WindowId,
+    DispatchPhase, DisplayId, Entity, EventEmitter, ForegroundExecutor, Global, KeyBinding, Keymap,
+    Keystroke, LayoutId, Menu, PathPromptOptions, Pixels, Platform, PlatformDisplay, Point,
+    PromptBuilder, PromptHandle, PromptLevel, Render, RenderablePromptHandle, SharedString,
+    SubscriberSet, Subscription, SvgRenderer, Task, TextSystem, View, ViewContext, Window,
+    WindowAppearance, WindowContext, WindowHandle, WindowId,
 };
 
 mod async_context;
@@ -525,6 +525,14 @@ impl AppContext {
         self.platform.primary_display()
     }
 
+    /// Returns the display with the given ID, if one exists.
+    pub fn find_display(&self, id: DisplayId) -> Option<Rc<dyn PlatformDisplay>> {
+        self.displays()
+            .iter()
+            .find(|display| display.id() == id)
+            .cloned()
+    }
+
     /// Returns the appearance of the application's windows.
     pub fn window_appearance(&self) -> WindowAppearance {
         self.platform.window_appearance()