Re-enabled code action support through the experimental server

[scohen]

This was removed when we backed out the change that allowed code actions. Re-enabling them, but only if experimental support is on.

[scohen]

@lukaszsamson I've been using this branch, and the code actions work really, really well.

[gmile]

@scohen out of curiosity, how does one enables this feature? I understand I would need to checkout elixir-ls locally, would you be willing to share the steps you're taking to make your editor use the locally checked out elixir-ls?

(I'm using nvim, but even if the steps are related to VSCode - I think it would help me connect the dots and replicate it for nvim)

[scohen]

@gmile Glad you asked:
to build elixir LS with the experimental server, just compile it as follows:

MIX_ENV=prod ENABLE_EXPERIMENTAL_SERVER=true mix elixir_ls.release -o ~/bin/

That will output the language_server.sh / language_server.bat files in your home directory's bin subdirectory. Then it's just a matter of updating nvim's configuration to point to that path rather than wherever it resides currently.
Conversely, you could overwrite the current installation by specifying the current installation's directory in the -o option.

After that, you should magically have the code action for replacing unused variables with underscored versions.