Adds a new explorerViewer sort order configuration item, barrelFirst

[AmbrosiaDevelopments]

This setting sorts barrel files (index.js, index.ts, etc.) in alphabetical order above all other files. Folders remain above all files including barrel files.

Partially addresses #27286 (still open but not specifically calling for this) and a comment requesting this feature on a now closed issue, #12345.

[msftclas]

All CLA requirements met.

[isidorn]

Thanks for this PR. However it is usually great to first start a discussion before imlpementing the whole PR.
We will not accept this since this is very javascript specific and not a lot of users requested for this.
Leaving this open as we might change our mind in the future. Thanks

[AmbrosiaDevelopments]

That's fair enough. It doesn't specifically look at file extensions like .ts or .js, just any file starting with index. Would you be able to advise if this functionality (changing file explorer sort order) is possible from an extension? I have looked for how to achieve it but found nothing at all so far about changing file explorer like that.

[isidorn]

Unfortunetely this is not possible using an extension. And that is one of the reason why I will keep this PR open for now, since there is no other way to achieve this.

[isidorn]

Clossing as out of scope.
Thank you again for your PR.

[AmbrosiaDevelopments]

Is there another way to achieve this yet? Is there a plan to open up API to allow this or anything further?

[isidorn]

There is currently no way to achieve this. We do not plan to open up the API.
There is this feature request which you can comment on and upvote #27286

[AlanLeeMoven]

Recommend changing 'barrel' to 'index' in every use across this PR to make the name more intuitive and specific. Hoping this gets resolved some day...