This PR adds the ability for the Tailwind language server
(`tailwindcss-language-server`) to be controlled by the
`language_servers` setting.

Now in your settings you can indicate that the Tailwind language server
should be used for a given language, even if that language does not have
the Tailwind language server registered for it already:

```json
{
  "languages": {
    "My Language": {
      "language_servers": ["tailwindcss-language-server", "..."]
    }
  }
}
```

Release Notes:

- N/A