Add support for Godot's node tree

[chiepomme]

This PR adds LINQ to tree support for Godot's node tree.
I copied Unity's LINQ to tree support and modified them for Godot. I tested it on Godot 4.4.

I'm worried about the way to change the behavior of NodeTraversable.
It uses includeWindow field to decide whether it traverses over a root Window or not.

ZLinq/src/ZLinq.Godot/NodeTraversable.cs

Line 15 in 50180a8

readonly bool includeWindow;

ZLinq/src/ZLinq.Godot/NodeTraversable.cs

Lines 29 to 42 in 50180a8

	public bool TryGetParent(out Node parent)
	{
	var maybeParent = node.GetParent();
	if (maybeParent is null || (!includeWindow && maybeParent is Window))
	{
	parent = default!;
	return false;
	}
	else
	{
	parent = maybeParent;
	return true;
	}
	}

Is it OK? or should I make a dedicated struct like NodeTraversableIncludingWindow?

[neuecc]

Thank you very much!
I'm glad you like the Godot support suggestion.
Regarding the includeWindow feature, it seems to only affect Ancestors, which I think creates a good balance in terms of usability.
I'll merge it right before the next release and include it in the release.

[chiepomme]

Thank you for reviewing.
Could you wait for my next commit? I completely forgot child windows like pop-ups. I think we should not ignore windows in Godot, so I'll remove the includeWindow option.

[chiepomme]

I removed includeWindow option, and added an example to get ancestors under current Window.

[neuecc]

Thank you.
Since there are major changes in #28, the Traversable interface will change significantly.
I'd like to merge this before conflicts occur, then adapt it to the new interface before releasing.