Add Haskell language server support

[morganthomas]

No description provided.

[locallycompact]

We can have this in a few hours if we don't need plugins, otherwise we are blocked everything successfully building against 9.4

[morganthomas]

@marcinbugaj , see above. Do we need HLS plugins?

[marcinbugaj]

The most crucial features are: jump to definition, find references, type information on hover, highlighting references. According to: https://haskell-language-server.readthedocs.io/en/latest/features.html the aforementioned features are provided by ghcide. Features like import refining, formatting, linting are provided by other plugins. It seems to me that we can settle for those crucial features and omit plugins.

[marcinbugaj]

On the other hand here: https://haskell-language-server.readthedocs.io/en/latest/support/plugin-support.html ghcide functionality is described as being a plugin. It seems we need at least core ghcide plugins/tier 1 plugins. From the attached link it follows that most non-tier1 plugins are not supported for ghc 9.4.