Unify tool version manager detection

[zachallaun]

We currently do tool version detection (asdf/mise/system) twice: once in bash when we boot the server, and once in Elixir when we boot the remote control node:

• https://github.com/lexical-lsp/lexical/blob/main/bin/activate_version_manager.sh

• lexical/apps/remote_control/lib/lexical/remote_control.ex

  Line 128 in d441dd2

  def elixir_executable(%Project{} = project) do

It's fine if we have to do this twice, but we should find a way to share code here. There was a reason I didn't do this immediately when I rewrote the bash side of things, but I don't recall what it was.

[zachallaun]

Here's one way this could be done:

• start_lexical.sh can be modified to pass the full path as an argument to boot.exs:

  $elixir_command \
    --cookie "lexical" \
    --no-halt \
    "$script_dir/boot.exs" \
    "$(which $elixir_command)"

• This could then be passed Lexical.Server.Boot.start which could set Application.put_env(:server, :elixir_executable, elixir_executable) (or perhaps Application.put_env(:lexical, ...)?)
• This app env var could then be read when starting the remote control node instead of going through elixir_executable/0

Doing this would, I think, guarantee that the remote control node always be started using the exact same Elixir executable that started the server. I also believe it would be more future-proof: while Lexical doesn't currently support Windows, this removes a code-path in RemoteControl that assumes a unix-like environment.