Hide plugin class filenames in new node selector

[innovate-invent]

As a plugin developer I am having to use the add_custom_type() function over the class_name and @icon features of GDScript if I don't want the sub-optimal user experience of the filename of the script to be included in the new node selector.

Ideally the experience should be consistent regardless of using add_custom_type vs class_name. I propose that the filename be moved to a tool-tip of a new "plugin" icon right justified to the node name. Below is a mock of the proposed UI:

Additionally, it would be more useful to the user to display the plugin name within the tool-tip along with or instead of the filename.

This is a continuation of the chat conversation here: https://chat.godotengine.org/channel/editor?msg=hsdk5fzi6eKjCTqhQ

[Calinou]

I've opened a pull request to implement this: godotengine/godot#90548