Add visibility mode to as_sortable_control()

[KoBeWi]

as_sortable_control() introduced more problems than it's worth it tbh, most of which come from unifying what's considered a sortable child to always use is_visible_tree(). This PR breaks the unification by introducing visibility mode to this method. By default it checks for is_visible_in_tree(), but it can be is_visible() or no visibility check, depending on needs. This allows to apply it in some classes that couldn't use it before.

Fixes #92618
Fixes https://chat.godotengine.org/channel/gui?msg=dmJWbcbv5amvaLMi9
Fixes #92812 (not tested)
(this time it was PanelContainer)
EDIT:
Also ScrollContainer: Fixes #92614 Supersedes #92714

Alternatives are making sure that containers don't break when using is_visible_in_tree() (unlikely, given how Control sizing is unsolved Godot problem since forever), or reverting #91613.

[kitbdev]

I was thinking instead of having modes, have an is_visible_in_tree() guard in all Container's sort children notifications, since no logic needs to run in sort children if the Container itself is not visible. Then there's no need to check if each child is visible in tree, they can just check is_visible() and the Container handles the is_visible_in_tree() part.

Also, missing some Containers like ScrollContainer, AspectRatioContainer, CenterContainer, GraphFrame, FlowContainer, and GridContainer.
GraphNode should also be set to visible mode for it's minimum size.
I think all minimum size checks should use is_visible() instead of is_visible_in_tree().

[KoBeWi]

For now I only fixed PanelContainer issue, other changes are bonus refactoring. I tried to keep the current behavior (TabContainer change was an oversight), any other improvement can be done later.

[AThousandShips]

Does this also solve:

• [4.3 Beta 1] AnimationPlayer animation list scroll bar disappears after first use. #92614

[KoBeWi]

Now it does.

[AThousandShips]

LGTM, all the get_child cases match cleanly and code looks good

[akien-mga]

Thanks!