Add Node.translation_domain

[Synzorasize]

Describe the project you are working on

I am using Translations as a resource in my project.

Describe the problem or limitation you are having in your project

This was inspired by godotengine/godot#99258.

If a user wants to split their Translation resources by topic or want to be able to access two Translations of the same locale, then they can use TranslationDomains. However, currently, they can only set a Node to use a specific domain through code, which may be inefficient for some workflows.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

If it is able to be set in the inspector, then that would save the user from having to do it in code since it would be accessible in the inspector.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

There is already _translation_domain, but that can't be used directly, of course. Therefore, if translation_domain is added, then it can be set whenever _translation_domain is changed and it would automatically be seen in the inspector.

If this enhancement will not be used often, can it be worked around with a few lines of script?

You can use _get_property_list for this, but it would be too complex for some workflows.

Is there a reason why this should be core and not an add-on in the asset library?

TranslationDomains were originally created for editor plugins to use, but I think it could be useful outside of there, too.