Open new windows with a default size and position (#9204)

This PR changes GPUI to open windows with a default size and location,
and to otherwise inherit from their spawning window.

Note: The linux build now crashes on startup.

Release Notes:

- N/A

---------

Co-authored-by: Nathan <nathan@zed.dev>
Co-authored-by: Ezekiel Warren <zaucy@users.noreply.github.com>

crates/gpui/src/app.rs

@@ -520,6 +520,11 @@ impl AppContext {
         self.platform.displays()
     }
 
+    /// Returns the primary display that will be used for new windows.
+    pub fn primary_display(&self) -> Option<Rc<dyn PlatformDisplay>> {
+        self.platform.primary_display()
+    }
+
     /// Returns the appearance of the application's windows.
     pub fn window_appearance(&self) -> WindowAppearance {
         self.platform.window_appearance()