Provide encoding property for editor extensions.

[ArcticLampyrid]

Provide encoding-related APIs for editor extensions.
At least we should add a simple read-only encoding property to TextDocument.
It seems easy since the encoding is already displayed in VSCode's status bar.

This is a simplified #824, but I believe it's needed to reopen an issue,
as most developers are not focusing on old issues.

[jrieken]

/duplicate of #824

[vscodenpa]

Thanks for creating this issue! We figured it's covering the same as another one we already have. Thus, we closed this one as a duplicate. You can search for similar existing issues. See also our issue reporting guidelines.

Happy Coding!

[ArcticLampyrid]

/duplicate of #824

So any progress?