Implement `editor-service`

[rope-hmg]

I don't mind having a go at this.

Is schema v5 mentioned in the README finalised yet?

If not, ping me a message once it is and I'll have a go at a PR.

[watsom27]

Looks like dprint is now using schema v5 as of https://github.com/dprint/dprint/releases/tag/0.29.0

[rope-hmg]

I've made some progress on this, but it doesn't work just yet. The messages look correct according to the docs I could find, but having trouble communicating on stdin without getting stuck in an infinite loop. I'm not super familiar with Python's process communication APIs.

You can see the progress here: https://github.com/rope-hmg/dprint-sublime