Propagate previously unused NOTIFICATION_WORLD_2D_CHANGED, make CanvasItem/CollisionObject2D use it

[spacechase0]

(Master version of #52761)

I took into account the feedback on the previous PR (and put one comment there, since a suggested change didn't work).

New test project (converted one from #52423): LocationTest.zip (One small difference is I had to change the default environment background color for the 3D test so you could actually see things, since for some reason with master it doesn't render correctly, and everything is black instead. Not sure what the deal with that is.)

Bugsquad edit:

• Fixes Separate Viewport/World2D with another viewport sharing the World2D causes physics errors, no rendering #52423

[reduz]

So, this is actually really good and needed, the problem is that in 3D you have ENTER_WORLD and EXIT_WORLD notifications and this PR would make 2D work inconsistently with that.

That said, I think the functionality in this PR is better, and changing the 3D notifications to a single NOTIFICATION_WORLD_3D_CHANGED would be more fit, as in most cases you could just use enter/exit tree and handle the 3D world change separately.

So,would you be up to do this change on the 3D side too to make it remain consistent?

[spacechase0]

Sorry for the huge delay in response on this - is changing 3D to match still something that is desired since Godot 4 is in beta now? Or should the 2D functionality here be made to match? Or neither?

[KoBeWi]

IMO the PR is fine in the current form. It's too late to change the 3D side, so we'll have to live with inconsistency I guess.

[spacechase0]

Should I squash the PR into 1 commit as well? Or at least the last 3 commits (since they just say "Update ", since I forgot to change them before committing in the web interface).

[KoBeWi]

Squash everything into 1 commit.

[spacechase0]

Okay, should be good to go.

[KoBeWi]

Suggested change

	if (v) {
	if (v->world_2d.is_valid()) {
	if (v && v->world_2d.is_valid()) {

Can be simplified.

[akien-mga]

I guess this was written like this to be consistent with 3D:

Viewport *v = Object::cast_to<Viewport>(p_node);
if (v) {
        if (v->world_3d.is_valid() || v->own_world_3d.is_valid()) {
                return;
        }
}

Which would need to become if (v && (v->world_3d.is_valid() || v->own_world_3d.is_valid())) too.

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉