Cannot export Variant in GDScript 2.0

[Xrayez]

Godot version:
a4f70d7

OS/device including version:
Windows 10.

Issue description:
Try to export Variant:

This should be possible because it's possible to do in C++, as seen in https://github.com/godot-extended-libraries/json, with PROPERTY_USAGE_NIL_IS_VARIANT (which is not exposed to scripting either).

See also godotengine/godot-proposals#1740.

Steps to reproduce:
Write this script:

class_name JSONResource extends Resource

@export var data: Variant
@export var json: String

Minimal reproduction project:
godot_export_variant.zip

[vnen]

I think this would require a change in the inspector to allow the user to actually set some value. Like what was done in #33080.

[Xrayez]

Could be implemented something similar to what I described in #43238. I've actually implemented an entire VariantResource for this purpose in Goost: goostengine/goost#30.

Looking at #33080, that's basically an editor implementation of VariantResource, just the other way around. 👀

[BasilYes]

Something about this issue? Values in dictionaries work like Variant could be.

[dalexeev]

@BasilYes See #33080. The PR needs salvation/re-implementation.