Make vscode/hls compatible with SPJ

@simonpj had a few issues when setting up VSCode with HLS:

1. Setting up VScode with WSL2 requires a lot of work: https://code.visualstudio.com/docs/remote/wsl-tutorial
we should document that better or maybe automate it
2. a lot of HLS plugins that impact performance are enabled by default and as such slow down working on big codebases like GHC. Adjusting this should be documented well. The GHC repository could also include a project-specific vscode config file that does this for all developers.
3. confusing popups, e.g. https://github.com/haskell/vscode-haskell/pull/621

@fendor @runeksvendsen