FormatOnSave: modified

[saltcod]

VSCode introduced the concept of formatOnSave for just the parts of the file you changed a while back:
"editor.formatOnSaveMode": "modifications",

Wondering if such an option would work here?

We have some giant legacy files that would create huge diffs if we turned this on. Would love to be able to use this for new stuff that we write in those files though.

Thanks for this plugin. Extremely useful.