Experiment with overriding the menu with css.

[roundhill]

Enables the useShadowDOM flag, and tweaks the menu with CSS to add styling and remove the last menu item.

To Test

• Right-click on web and electron in light and dark mode.
• The "Command Palette" menu should be gone.
• The menu should look nice and work :)

[codebykat]

Okay this was a good backup plan 🙇 buuuuut I feel like hacking the CSS is a little too fragile (and I'm not sure what other effects the removal of the shadow DOM might have later on). I managed to find a different hack that feels a tiny bit less terrible: https://github.com/Automattic/simplenote-electron/pull/3183/commits/b6e8303638eafa8b7e80c98e24a4ea8b29abc41c