Integrate Scene Unique Nodes toggle in Node renaming process

[Mickeon]

Describe the project you are working on

Your typical 2D Godot project, peeking at upcoming Godot 3.5 features.

Describe the problem or limitation you are having in your project

Note: This proposal may go hand-to-hand with #4494

#4096 has been approved and Scene Unique Nodes have been implemented. Neat!

This feature is technically very functional. As is currently, however, it lacks a bit of polish.
Addressed in this proposal, there's several minute annoyances I find with the way it is currently enabled and disabled on any given Node.
The contextual menu of a Node is currently extended, both vertically and horizontally, by the relatively long string "Access as Scene Unique Name", a toggle whose special purpose awkwardly separates it from the other options. Indeed, the Unique toggle is inserted right in the middle of other, more general use options.
In other languages, this string could potentially be even longer, too.

That may sound reasonable, but as a result of the large list, its special presence can feel overbearing, especially for beginning users.
And that's not to mention the "%" button next to an Unique Node, which renders the act of toggling off from the contextual menu completely redundant!

I do agree, it doesn't seem like much at first glance, but as the Engine grows and more Quality of Life features are implemented, it is prone to contribute to clutter. The contextual menu is reasonably big as is.

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

When renaming nodes, a toggle button with the Unique symbol (currently "%") to the right (or left???) of the name should appear. Of course, it is disabled by default, and enabling it would further highlight the button.
Hovering over the button should also give a brief summary of the Scene Unique Node feature.

This efficiently "hides" the feature until it is most needed, in the process of renaming important nodes from their original class' name, for instance.

Discoverability is not an issue. Renaming nodes is part of the scene creating workflow, and part of what actually makes a node Unique is its very name. Its inclusion feels naturally fitting.

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

Very poor mock-up, just to further get the idea across:

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

It cannot.

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

Unique nodes are a core feature.