What problem does this feature solve?

• Return users the ability to write and use custom language service plugins
• Restore compatibility with volarjs/services (Related issue)

What does the proposed solution look like?

• Re-introduce volar.config.js. Related feat: support for custom language service plugins #1028, [Take Over mode][Suggestion] Add Setting to Force Suggestions Ordering #1005

Real world case

We have a typescript plugin extension which adds lots of useful but opinionated code actions/suggestions/completions etc.

Before v2 we were able to use volar.config.js to provide support for both .ts and .vue files. So, what we need is to be able to add a way to decorate vue language service methods:

How it was done before:

1. Get what we need to create plugin from context
2. Init plugin and save original LS
3. Create our 'proxy' plugin
4. Mutate language service to use our proxy