Use NSScreen to fetch primary display

According to Chromium source, `NSScreen::screens` should always get us
one display.

We made this change because we ran into panics caused by the previous
`unwrap()` when `CGGetActiveDisplayList` might return an empty list.

crates/gpui/src/platform/mac/window.rs

@@ -484,7 +484,7 @@ impl MacWindow {
 
             let display = options
                 .display_id
-                .and_then(|display_id| MacDisplay::all().find(|display| display.id() == display_id))
+                .and_then(MacDisplay::find_by_id)
                 .unwrap_or_else(MacDisplay::primary);
 
             let mut target_screen = nil;