Tree: add expand_all and collapse_all methods

[lupoDharkael]

Qt provides the methods expandAll() and collapseAll() for QTreeView.
It is an useful feature and it would be nice to have it in Godot :)

Here it is in action:

[groud]

How is this useful on the tree Itself ?
Such behaviors are usually applied to selected items, so I'd better make this a method of TreeItem, and not Tree.

[groud]

That being said, I'm not even sure this is required. I think I would simply define a call_recursive function to TreeItem, that would allow calling a function on a hierarchy of TreeItem.

So we could use tree_item.call_recusive("set_collapsed", true)

[lupoDharkael]

@groud having this in the Tree class means not having to reinvent the wheel everytime someone wants to have an "Expand all" button.
I think it's more user friendly to call a method in the Tree itself when you want to do global modifications to the items contained in the Tree.

This could be used in the editor itself as a way to improve usability in some parts where we have trees with multiples levels and the users could need to have a global view of everything (That should be treated in other issue).

Anyway, I'm open to other views/ideas about how to implement this.

[groud]

Well Godot's philosophy is simple : we add to the API things that are often needed OR hard to code. Expanding or collapsing all is probably 3 or 4 lines of code in GDscript, and such button is not that oftently used.

So, IMHO, there's no reason to add a shortcut in the API for that, unless we make this a more general purpose solution (like my call_recursive proposal). Otherwise, I think it's more API bloat than useful.

But other might disagree. :)

[lupoDharkael]

I like the idea of the call_recusive method and I might consider sending a PR for that :)
But I also think these methods are not mutually exclusive.
Maybe the discussion tag should be added to this PR (or is an issue a better place to discuss this?). Let's see what others think about this.

[lupoDharkael]

I'm closing this as I'm working on the call_recursive() solution.