macos: fix window.titleBarStyle on macOS

The commit fixes the `window.titleBarStyle` handling on macOS which would otherwise cause the menu to be completely removed and difficult to recover for users.

Signed-off-by: vince-fugnitto <vincent.fugnitto@ericsson.com>

packages/core/src/electron-browser/menu/electron-menu-contribution.ts

@@ -157,6 +157,9 @@ export class ElectronMenuContribution extends BrowserMenuBarContribution impleme
         });
         this.preferenceService.onPreferenceChanged(change => {
             if (change.preferenceName === 'window.titleBarStyle') {
+                if (isOSX) {
+                    return; // the `window.titleBarStyle` preference is a no-op on macOS.
+                }
                 if (this.titleBarStyleChangeFlag && this.titleBarStyle !== change.newValue && electronRemote.getCurrentWindow().isFocused()) {
                     electron.ipcRenderer.send(TitleBarStyleChanged, change.newValue);
                     this.handleRequiredRestart();

packages/core/src/electron-main/electron-main-application.ts

@@ -500,7 +500,7 @@ export class ElectronMainApplication {
         app.on('window-all-closed', this.onWindowAllClosed.bind(this));
 
         ipcMain.on(TitleBarStyleChanged, ({ sender }, titleBarStyle: string) => {
-            this.useNativeWindowFrame = titleBarStyle === 'native';
+            this.useNativeWindowFrame = isOSX || titleBarStyle === 'native';
             const browserWindow = BrowserWindow.fromId(sender.id);
             if (browserWindow) {
                 this.saveWindowState(browserWindow);