Fix Container pending_sort and "Saving Scene" ProgressDialog size.

[WhalesState]

Fixes: #92971

Since both issues are closed, and each one produces the other, it's better to fix both at the same time.

If this ever leads to any other issues that can't be fixed by deferring a sort children notification call, please tag me.

[akien-mga]

I'm confused, we already merged fixes for these issues. Your branch seems to be based off an earlier version of the master branch, so you don't have #93008. I'm not sure why it doesn't raise a merge conflict.

[WhalesState]

I have restored the branch after deletion, then i pressed update branch because it was already merged before so there was no commits ahead master, and when i opened the branch i didn't find the changes was reverted, so i just pressed undo last commit and i force pushed the changes. I also was confused because the last commit wasn't my fix, there was like 60 other commits.

[WhalesState]

I can't reproduce #92971, seems like it only happens with ProgressDialog.
We will need a MRP if it happened again after merging this pull request.

I have tried the same code in _ready(), _enter_tree() and _init() and it only calls sort children once every time i add the VBoxContainer -> Container2 as a child.

[WhalesState]

Sorry about the confusion, I just thought my fix was reverted because i used to see that happens when a pull request causes regression.
This also fixes the "Save Scene" dialog issue because i think the issue is not related to the Container class.

[akien-mga]

To clarify, #92971 was already fixed by #93008.

What bug is this PR aiming to solve?

[WhalesState]

Nothing, I reproduced the issue with this script to understand, Sorry -_-

extends Control


func _ready():
	var container = Container2.new()
	container.set_anchors_and_offsets_preset(PRESET_FULL_RECT)
	var popup := PopupPanel.new()
	popup.exclusive = true
	add_child(popup)
	popup.add_child(container)
	popup.size = Vector2(340, 256)
	popup.popup_centered()
	popup.hide()
	popup.remove_child(container)
	await get_tree().create_timer(1).timeout
	popup.add_child(container)
	popup.popup_centered()


class Container2:
	extends VBoxContainer
	
	
	func _init():
		for i in range(5):
			var button = Button.new()
			button.text = "Button %s" % i
			add_child(button)