haskell-language-server starts up slowly

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

I've set up a no-op project with the following files:

```cabal
-- foo.cabal
cabal-version: 2.4
name: foo
version: 0

library
build-depends: base
exposed-modules: Foo
```

```haskell
-- Foo.hs
module Foo where
```

With a _warm_ build, that is, after a `cabal build` at the command line, followed by an opening and closing of `Foo.hs` once (after letting haskell-language-server initialize), I observe the following timings upon opening `Foo.hs`:

where "processing" and "setting up" occur in parallel after "initializing" is complete.

"Initializing" here is the time between the client sending the "initialize" RPC request to haskell-language server and receiving a response.

"Processing" and "setting up" are just what haskell-language-server is reporting it's doing via progress handlers.

## Describe the solution you'd like

Well, I'd like this to go much faster :) Or, at least, I wanted to draw attention to the slow startup time, in case it was not yet on anyone's radar who might be able to diagnose and improve.

Thanks!