On macOS, set that we prefer tabbing

Winit now supports tabbing identifiers, thus set that we prefer tabbing,
in particular it'll make windows tab when using the same tabbing identifiers,
which is desirable for the end users.

src/platform_impl/macos/window.rs

@@ -48,7 +48,7 @@ use super::appkit::{
     NSApp, NSAppKitVersion, NSAppearance, NSApplicationPresentationOptions, NSBackingStoreType,
     NSColor, NSCursor, NSFilenamesPboardType, NSRequestUserAttentionType, NSResponder, NSScreen,
     NSView, NSWindow, NSWindowButton, NSWindowLevel, NSWindowSharingType, NSWindowStyleMask,
-    NSWindowTitleVisibility,
+    NSWindowTabbingMode, NSWindowTitleVisibility,
 };
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
@@ -362,6 +362,7 @@ impl WinitWindow {
 
             if let Some(identifier) = pl_attrs.tabbing_identifier {
                 this.setTabbingIdentifier(&NSString::from_str(&identifier));
+                this.setTabbingMode(NSWindowTabbingMode::NSWindowTabbingModePreferred);
             }
 
             if attrs.content_protected {