Improve time to close scene with many 3D gizmos

[aaronp64]

Changed EditorNode3DGizmoPlugin::current_gizmos from List to HashSet, to avoid having to iterate through all gizmos when ~EditorNode3DGizmo unregisters itself. Fixes the scene closing slowness in #94648

[aaronp64]

Didn't notice this earlier, but it looks like HashSet doesn't maintain insert order when an element is removed. If an element is removed, and the last element gets moved from after the index in Joint3DGizmoPlugin::incremental_update_gizmos to before it, it won't be redrawn until the next loop around. Might not be an issue, since it still gets redrawn eventually. Maybe SelfList would be a better option here?

[Hilderin]

I tested these modifications and I confirm that it helps a lot with the performance on opening and closing a scene from the editor.

Made a little MRP with 10000 cubes in the scene 100x100x10.tscn:
test-godot-editor-gizmo-performance.zip

Opening the scene:
Godot 4.3 rc3: 10 sec
This PR (in debug): 3-4 seconds

Closing the scene:
Godot 4.3 rc3: 18-20 seconds
This PR (in debug): 2-3 seconds

Careful, don't open another scene before testing because the performance will degrate caused by DynamicBVH::insert.

[Hilderin]

Might not be an issue, since it still gets redrawn eventually. Maybe SelfList would be a better option here?

I think it will be more performant to keep the HashSet since the main performance issue was the lookup and the removal of the gizmo objects. The lookup of thousand of objects in a SelfList will probably be very bad. I'm not concerned with the sort that is not kept when adding or removing gizmos, the timer will eventually redraw all the gizmos, as you said.

[Hilderin]

Everything sounds good to me.

[akien-mga]

Code changes make sense to me.

[akien-mga]

Thanks!