[3.x] Fix top level CanvasItem visibility

[timothyqiu]

This PR first reverts the backported #57684 (part of #57900) and #58386.

#57684 was backported mainly because it solves a bug where

CanvasLayer could propagate its visibility to CanvasItems that were separated by plain Nodes.

But after inspection these days, I think that is the expected behavior. CanvasItems that are explicitly marked as top level or have a non-CanvasItem parent were handled together as "top level", and they are logically parented to the nearest ancestor CanvasLayer or Viewport world canvas. See CanvasItem::_enter_canvas().

After the revert, the only problem is that CanvasLayer visibility propagation was only propagated to direct child CanvasItems. Fortunately, all these "top level" nodes are in a group called root_canvas{canvas_rid}, so moving the propagation logic into a call_group() is all that have to be done I think.

The editor gizmo fix from the reverted 642591b is kept.

---

I also stopped propagation onto explicitly top level CanvasItems because:

• Their logical parent is a CanvasLayer.
• For CanvasLayer, we propagate to these CanvasItems with call_group().
• There was previously a comment:
  

  godot/scene/2d/canvas_item.cpp

  Lines 385 to 387 in 6b4d7d2

  	if (c && c->visible) { //should the toplevels stop propagation? i think so but..
  	c->_propagate_visibility_changed(p_visible);
  	}

• Previously, the visibility of CanvasItems are only controlled by their logical parent inside VisualServer. So propagating onto top level nodes won't actually change anything.

---

Tested recent regressions like #58251, #58315, and #58782. They are not reproducible.

Fixes #58782

[akien-mga]

It would be clearer for the Git history if you could do this as actually git revert commits + another commit on top with your further changes.

[timothyqiu]

It would be clearer for the Git history if you could do this as actually git revert commits + another commit on top with your further changes.

The backport of #57684 is part of #57900. It can only be reverted manually. Should I do that as a separate commit too?
OK, I'll do a fake revert commit ;)

[akien-mga]

I meant you could revert this commit no? f49ffe4

Ah though I guess you wanted to keep some of the changes of that commit. It's fine as is :)

[akien-mga]

Thanks!

[timothyqiu]

I meant you could revert this commit no? f49ffe4

#57900 backports 3 PRs in that one commit f49ffe4. It's the last one of the three that needs revert. CanvasLayer visibility is kept.

I think I should have made that backport PR 3 separate commits in the first place :(