Support *.dib format for manage notebook file that only code snippet exclusive.

[Creta5164]

I found out that the ipynb format includes the contents of the execution results in the file.

However, I felt that it creates too many changes to the file, and makes it difficult to manage the version or resolve conflicts in the notebook file itself in the repository.

So I would like to support the dib format of .NET interactive, which does not use it.

[mstevenson]

This is a good suggestion, I'm not very familiar with the dib format but I agree that it appears better for version control. Is this a feature that you're currently working on? If not, I'd be glad to tackle it.

[Creta5164]

@mstevenson Yeah I think so but I haven't touched it because I thought it'll easily break compatibility.

[mstevenson]

@Creta5164 I did a quick pass on this: #6 adds .dib while preserving backwards compatibility with .ipynb. The Unity tool continues to use the Jupyter format internally and converts to and from .dib format during save and load.

I've only lightly tested this, so I'll leave the PR open until I can run some more extensive tests.

[Creta5164]

@mstevenson I'll try it soon if I have some time, I'll update this issue if there's no problem with it.

[Creta5164]

Hey, I've just got finally have chance to try it, it has compile error in our ends unfortunately.

Library\PackageCache\com.mstevenson.unitynotebook@1bfa31c3a8\Editor\UI\CodeArea.cs(19,20): error CS1061: 'TextEditor' does not contain a definition for 'isMultiline' and no accessible extension method 'isMultiline' accepting a first argument of type 'TextEditor' could be found (are you missing a using directive or an assembly reference?)

We are using 2022.3, so I figured out about that API, it's introduced in 2023.1, I'll probably make PR about this backward compatibility.

https://docs.unity3d.com/Manual/WhatsNewUnity6.html