Support generating LSIF and/or SCIP index.

## Is your enhancement request related to a problem? Please describe.

[Server Index Format (LSIF)](https://lsif.dev) and its successor [SCIP Code Intelligence Protocol (SCIP)](https://github.com/sourcegraph/scip) is a language-agnostic index format like ctags. It's developed by and used in sourcegraph, which provides web interfaces for code browsing with code navigation. Though there is already an [LSIF implementation for Haskell](https://github.com/mpickering/hie-lsif), it has not maintained for long time.

## Describe the solution you'd like

Adding a feature to generate SCIP index to this.
Also, we can get LSIF index with the [SCIP to LSIF converter](https://github.com/sourcegraph/scip/blob/main/docs/CLI.md#scip-convert)

## Describe alternatives you've considered

Implement as a separated project.

## Additional context

I know that [rust-analyzer](https://rust-analyzer.github.io/) had [this functionality](https://github.com/rust-lang/rust-analyzer/blob/master/crates/rust-analyzer/src/cli/scip.rs), but I can't find any document...

[Discussion at clangd](https://github.com/clangd/clangd/issues/1340)