Make menus/separator spacing consistent with Breeze
This complements a recent minor spacing change in breeze@ee5cc384 by restoring the spacing for separators, and balances the spacing for menu items so they are visually within pixels of the Breeze Qt theme.
Up to now, there were no spacing for separators, and I had stuck with breeze-gtk
5.20.5 all this time since the menu spacing became too wide around >=5.21.
This should fix https://bugs.kde.org/show_bug.cgi?id=433158.
BUG 433158
Screenshots
- Left: Qt: A replica of Pluma (GTK)'s menu bar / File menu (.ui file)
- Right: GTK 3 app, MATE Pluma