Fix autoload node cannot be accessed by plugin on start-up

[Hilderin]

• Fixes Autoloaded singleton cannot be accessed at early phase during editor plugin start-up during editor start-up #77037

I was testing if #92667 fixes the issue #77037. Unfortunately, it does not.

But, I think the issue was caused by that:

• When the editor is already running, calling add_autoload_singleton creates and adds the autoload into the scene tree directly. So, the get_node("/root/" + AUTOLOAD_NAME) works fine. The autoload is now in the project settings.
• When the editor is restarted, now that the autoload is in the project settings, the autoload is created before the plugin init but the add_child to the scene is deferred in EditorAutoloadSettings::init_autoloads:

callable_mp((Node *)get_tree()->get_root(), &Node::add_child).call_deferred(info.node, false, Node::INTERNAL_MODE_DISABLED);

Then, the plugin is initialized and added to the scene and oups, we are in a situation where the plugin _entre_tree is executed before the autoload is added the the scene.

So, the solution was to call add_child directly, no deferred in EditorAutoloadSettings::init_autoloads. I think that was not possible before #92303 because the autoloads were created way earlier.

This is a simple MRP to reproduce the problem:
test-godot-plugin-autoload-with-resource.zip

Note: This is an alternative solution to #86453 that fixes the problem without changing any loading order.

[apples]

Can confirm that this fixes the issue 👍

My test project is quite similar to the MRP.

[akien-mga]

Seems fine to me if it works.

I checked the blame and this call was added deferred in 2018 by @vnen in 55b4b30, I don't know if you remember why it had to be deferred or if this was done just in case.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 4.3.1.