Make Popup Menu Divider-Lines Consistent

### Your use case

*Full divider*

*Full divider*

*Inset divider*

#### What would you like to do?
Make popup menu divider-lines consistent:
Inset dividers in popup menus
#### Why would you like to do it?
Visual consistency.

### Have you considered any alternatives?

Make popup menu divider-lines consistent:
full-width dividers in popup menus.

### Additional context

This (standardise) may also apply to font and icon size as these differ between left and centre panel

No file or test is identified. Compare popup menus in the left and centre panels, starting from the popup-menu UI entry points, and determine whether inset or full-width dividers are the intended standard; done means the divider lines are visually consistent without introducing differences in font or icon sizing.

Written by the indexing model from the issue text.