Test for #29024

• windows @bpasero
• windows @octref
• linux @Tyriar

Complexity: 4

Summary
On Windows and Linux, users can now opt in to use the custom titlebar that has been available on macOS for some time. With this change, we have implemented a new HTML-based menubar that is more accessible than the Electron version as well as just looks nicer. In order to match the new menubar, menus throughout the workbench are now using the same menu widget.

Test

1. First, set window.titleBarStyle to custom and restart Code.
2. Use the new titlebar and window controls.
3. Use the new menubar.
4. Try out menus throughout the workbench.

Things to verify

• Do the window controls work as expected?
• Can you navigate the menubar with a keyboard?
• Can you navigate the menubar with the mouse?
• Does the menubar honor settings like window.enableMenuBarMnemonics and window.menuBarVisibility?
• Accessibility with screen readers
• Do the actions in the menubar as well as menus throughout the workbench actually work?

See existing issues here for dupes Menu and Accessibility