Ability to extend base scene script easily for inherited scenes

[kubecz3k]

Issue description (what happened, and what was expected):
When we are creating new inherited scene, it would be cool if we could have an option to automatically create script that's extending base scene script. I think this extended script could be saved in the same location where inherited scene is saved, under the same name but with gd extension.
Simple switch, something like "create extended script: on/off" inside this dialog window in which we are pointing base scene, would be enough.

related issue: #4584

[MarianoGnu]

I belive an option on contextual menu is enought for this
If no script:
-create script
If has script
-edit script
-extend script

This should not only work for scene instance, but for every node with a script assigned

[kubecz3k]

@MarianoGnu yeah #4584 is about this.

[kubecz3k]

If anyone is interested in this, I made a plugin that adds 'inherit node' button. It's called 'Smart scene extender' and is available via asset store.

[Calinou]

Feature and improvement proposals for the Godot Engine are now being discussed and reviewed in a dedicated Godot Improvement Proposals (GIP) (godotengine/godot-proposals) issue tracker. The GIP tracker has a detailed issue template designed so that proposals include all the relevant information to start a productive discussion and help the community assess the validity of the proposal for the engine.

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