Add support for adding/removing editor plugins

[dsnopek]

This depends on godotengine/godot#77010

It allows adding or removing editor plugins from GDExtension, in a way that's very similar to adding them in a Godot module.

Here's some example code from a test GDExtension:

void initialize_summator_types(ModuleInitializationLevel p_level)
{
	if (p_level == MODULE_INITIALIZATION_LEVEL_SCENE) {
		ClassDB::register_class<Summator>();
	}

	if (p_level == MODULE_INITIALIZATION_LEVEL_EDITOR) {
		ClassDB::register_class<MyEditorPlugin>();
		EditorPlugins::add_by_type<MyEditorPlugin>();
	}
}

void uninitialize_summator_types(ModuleInitializationLevel p_level) {
	if (p_level == MODULE_INITIALIZATION_LEVEL_SCENE) {
		EditorPlugins::remove_by_type<MyEditorPlugin>();
	}
}

Please let me know what you think!

Fixes #640

[akien-mga]

Thanks!

[Zylann]

I wonder why classes dont need to be unregistered (they are done automatically) yet plugins have to be unregistered manually?

[dsnopek]

@Zylann:

I wonder why classes dont need to be unregistered (they are done automatically) yet plugins have to be unregistered manually?

That's a good question!

It looks like ClassDB on the godot-cpp side is keeping track of the classes we register, and then GDExtensionBinding::deinitialize_level() is calling ClassDB::deinitialize() which is removing them.

We should be able to do the same thing for editor plugins! EditorPlugins in godot-cpp could keep track of what we've registered, and we could add a EditorPlugins::deinitialize() that removes them, and call it in GDExtensionBinding::deinitialize_level().

I'll add it to my TODO list! (Unless you want to make the PR for this?)

[Zylann]

Unless you want to make the PR for this?

Too busy on other things atm.

Thanks for adding this feature to GodotCpp, it was sorely missed :D