Fix the position and size of the Options menu across the editors

[afercia]

Description

The position and size of the Options menu across the editors is inconsistent:

1. The spacing from the right edge of the screen is different. The root cause is the different right padding applied to the container of the More button that opens the menu. Improve button spacing in the top right corner of the editor #40411 standardized this padding but then Clean up header toolbar metrics and responsive break points #56729 changed it again only in the Site editor. Also, the post editor changes this padding for small screens while the site editor doesn't.
2. The actual width of the menu depends on its content. It's a flexible width between 280 and 480 pixels. In the two editors the menu content is different. As such, the menu width differs. To me, visual consistency is more important than trying to accomodate width based on the content. I think there's two options here:

• Either enlarge a bit the width: there's no apparent reason why the minimum width must be 280 pixels. That's the width of the sidebars but this menu doesn't need to look like a sidebar.
• Make it have ea fixed width.

Step-by-step reproduction instructions

• Compare the Options menu in the Post editor and in the Site editor.
• Observe the spacing from the right edge of the screen is different by 2 pixels.
• Observe the position of the More button (the ellipsis) is different in the first place.
• Observe the width of the menu is different.

Screenshots, screen recording, code snippet

Screenshot: Options menu in the Post editor and in the Site editor:

Environment info

No response

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes