Free submenu children when clearing PopupMenu

[KoBeWi]

While doing something else, I noticed that PopupMenu doesn't free submenu children when calling clear(). This means for example that the Create New menu in filesystem is created every time you right-click, which results in infinite unused menus.

[YuriSizov]

I don't like this being the default and only option (which also makes this change compatibility breaking). It makes sense in the editor codebase, and in other code-first cases, but it conflicts with the node-first approach that some of our users prefer.

Say, you have a popup menu with a submenu, and you add both nodes in the editor UI. In the current form, what you see is what you get, and clearing the parent menu won't remove the submenu. You would only need to connect it as one of the items, which you need to do from code anyway.

With the proposed change clearing the items of the parent menu will remove the node that you've added to the tree visually. You will no longer get what you see, and you will have to recreate it from code every time. This just makes things harder for no reason, and it wastes a tiny bit of time recreating nodes.

As we discussed before, a flag can be added to the clear() method instead. I think it's still not an ideal solution, as we'd still be capable of missing the bugs this is trying to address. But I guess it's easier to spot if in the editor code we are forgetting to call clear() with true, which we would almost always want to do. So unless a better solution is suggested, the flag (off by default) would be acceptable.

[KoBeWi]

I could add a flag and make it on by default in C++ and off by default in GDScript (it's possible).

[YuriSizov]

I could add a flag and make it on by default in C++ and off by default in GDScript (it's possible).

Aye, it's possible, but it may be frowned upon. I remember we discussed a case like that before, though I don't recall any details.

[KoBeWi]

We use this for Node methods with internal children argument.

[YuriSizov]

Ah, right, that was it. Well, that works as well then.

[akien-mga]

Needs a rebase, then I guess it should be ready to merge.

[akien-mga]

Thanks!