Can we get an api to get the diff?

Hey,

when using this to format in an editor, I want to replace the smallest parts possible of the text buffer.
Currently I'm running elm-format on a file, get that whole string and need to do a diff against the file before the format.
https://github.com/elm-tooling/elm-language-server/blob/master/src/providers/documentFormatingProvider.ts#L40

It might help to improve runtime, if we can do this in elm-format.

Cheers

Start by reading the formatter integration referenced in src/providers/documentFormatingProvider.ts#L40 and the elm-format command or API entry point. Determine how formatted output is currently produced and what interface an editor would need to obtain a diff rather than a complete file. Done means an agreed, documented API exists and its behavior is covered by tests.

Written by the indexing model from the issue text.