Seperate MenuButton into Menu and MenuItem controls.

[Shadowblitz16]

Describe the project you are working on

A space voxel game, but that's not really relevant to the issue.

Describe the problem or limitation you are having in your project

None right now but I have experienced the problem in the past when trying to make a desktop editor in godot.

Basically Godot's MenuButton is both a Menu and a MenuItem control all wrapper up in one control.
This makes it harder to visualize the ui in the scene editor and hook up MenuItem clicked signals and you have to get the popup and hook them up by index.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Separate MenuButton into Menu and MenuItem controls.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Instead of something like this...

• Hbox
• • FileMenuButton
• • EditMenuButton

We would beable to define menus like this...

• HBox
• • FileMenuButton
• • • NewMenuItem
• • • • AMenuItem
• • • • BMenuItem
• • • OpenMenuItem
• • EditMenuButton
• • • RedoMenuItem
• • • UndoMenuItem

If this enhancement will not be used often, can it be worked around with a few lines of script?

It would be used way more often then the current solution because you could hook up MenuItem signals better.

Is there a reason why this should be core and not an add-on in the asset library?

It's already part of core but part of MenuButton,
Godot dev's said they didn't want to implement it due to performance concerns.
godotengine#1556