findExecutable in Wrapper.hs execute prebuilt's hls rather than 'cabal build''s output

## Is your enhancement request related to a problem? Please describe.
1. According https://haskell-language-server.readthedocs.io/en/stable/contributing/contributing.html#building-with-nix. Using nix-shell to execute wrapper.
2. Executing `cabal run haskell-language-server-wrapper lsp`
3. Code run to https://github.com/haskell/haskell-language-server/blob/be30f3eb5bba59c50c084a324d432bfc2df24837/exe/Wrapper.hs#L157
4. The `mexe` found by `findExecutable` turns out as following. Rather than exe from `dist-newstyle` which contains `cabal build`'s output.
```
mexes =
[ Just "/nix/store/x4njcm292dm8wgqjhxyp4jxcx77sz3x2-haskell-language-server-2.10.0.0/bin/haskell-language-server-9.8.4"
, Just "/nix/store/x4njcm292dm8wgqjhxyp4jxcx77sz3x2-haskell-language-server-2.10.0.0/bin/haskell-language-server"
]
```
5. The exes on nix store is added in here. Rather than `cabal build`'s output
https://github.com/haskell/haskell-language-server/blob/be30f3eb5bba59c50c084a324d432bfc2df24837/flake.nix#L71

## Describe the solution you'd like
1. Maybe upgrade the documentation https://haskell-language-server.readthedocs.io/en/stable/contributing/contributing.html#building-with-nix. Using nix to compile and startup Wrapper?
2. Maybe change `findExecutable` way to find the `cabal build`'s exe?
3. Maybe precompile tools chains than import? https://github.com/haskell/haskell-language-server/blob/be30f3eb5bba59c50c084a324d432bfc2df24837/flake.nix#L71

## Describe alternatives you've considered
Or I need help, Maybe my execution method has issue.

## Additional context
None.

Start with exe/Wrapper.hs around the referenced findExecutable call, then inspect flake.nix around line 71 and the Nix building documentation. Reproduce the cabal run command in nix-shell and determine whether the intended outcome is documentation, executable-selection behavior, or toolchain precompilation. Done means one chosen approach is specified and its behavior is verified.

Written by the indexing model from the issue text.