Setting up `jest-editor-support` as a language server

[seanpoulter]

I'm opening this issue as a place to discuss if/when we should set up jest-editor-support as a language server. If we start to look at testing unsaved documents, we're going to increase our IO and CPU loads which may be better suited to a language server.

Seems like it'd be useful to support:

• incremental updates to source files
• incremental AST updates (TS supports it, not sure about the Babylon parser)
• providing parsed test suite and test locations, names, etc. for any consumer (e.g.: a test result View like JUnit in Eclipse)
• incremental test result updates based on the files changed

Here's the relevant Extension docs for VS Code:

• Overview
• Example - Language Server

[Raathigesh]

This would be really useful and would allow us to build even more great tools on top of it. This could unlock some interesting possibilities for https://github.com/Raathigesh/majestic. I'm very much interested in contributing to this effort. Let me know how I can help.