macOS: Fix center window with fixed bounds size (#8475)

This PR fixes window showing up in the center of the monitor when
`center: true` option is provided.

The idea is to set the `window_wize` when creating the `window` using
`native_window.initWithContentRect_styleMask_backing_defer_screen_()`

Before: 

<img width="851" alt="SCR-20240227-qokf"
src="https://github.com/zed-industries/zed/assets/20229808/27494966-2e97-4771-8837-ccb6658ced78">

After:

<img width="1132" alt="SCR-20240227-qlmg"
src="https://github.com/zed-industries/zed/assets/20229808/439568da-d380-4331-8d19-cd501f211c4c">


Release Notes:

- N/A

crates/gpui/examples/hello_world.rs

@@ -23,7 +23,15 @@ impl Render for HelloWorld {
 
 fn main() {
     App::new().run(|cx: &mut AppContext| {
-        cx.open_window(WindowOptions::default(), |cx| {
+        let options = WindowOptions {
+            bounds: WindowBounds::Fixed(Bounds {
+                size: size(px(600.0), px(600.0)).into(),
+                origin: Default::default(),
+            }),
+            center: true,
+            ..Default::default()
+        };
+        cx.open_window(options, |cx| {
             cx.new_view(|_cx| HelloWorld {
                 text: "World".into(),
             })