Fix ADD_PROPERTY() calls in GDExtension C++ example to use correct syntax

[Calinou]

This matches how properties are declared in core Godot.

• See tutorials/scripting/gdextension/gdextension_cpp_example godot-docs-user-notes#36 (comment).

[dsnopek]

Thanks! Looks correct to me :-)

[paddy-exe]

LGTM

[mhilbrunner]

Thank you, and thanks for the reviews everyone! :)

[mhilbrunner]

Cherry-picked to 4.3 in #10038.

[Batodalaev]

Hello everyone.

FYI, https://docs.godotengine.org/ru/4.x/tutorials/scripting/gdextension/gdextension_cpp_example.html not updated yet.

For example this string:
ADD_PROPERTY("GDExample", PropertyInfo(Variant::FLOAT, "speed", PROPERTY_HINT_RANGE, "0,20,0.01"), "set_speed", "get_speed");
here must be removed "GDExample",

Something went wrong?
Or how much time should pass?

[paddy-exe]

@Batodalaev The translated docs are merged before every release candidate.