This restores the global app menu applet you can place in your panel.

Pretty much WIP, it's using a QStringList instead of a current model right now :D
Also the keyboard nav stuff with event filter doesn't fully work but it's usable already. Sometimes gets confused about which menu to use and goes blank, or clicking the same entry again after the menu closed doesn't work for some reason.

I have no idea how to deal with keyboard activation, however, and I don't recall how that worked in Plasma 4. I don't see how we could transfer Alt+F to e.g. "File" (and apparently Unity doesn't even do that?). There's an activation request signal which looks like it's for this exact purpose but I've never actually seen anybody emit it.

Only thing I could think of would be an Alt modifier only global shortcut that passes focus to the menu bar (forcing focus on the panel) and then you can navigate there using keys, or so.

To allow ToolButtons to shrink in a way they do I had to add a Layout.fillWidth: true for the ToolButtonStyle's label component. It's doing verticalAlignment: Text.AlignVCenter already which does nothing without a size anyway.