Raise a better error when using elixir with ref:v1.11.4

[axelson]

The errors in the following issues are similar:

• https://github.com/elixir-lsp/elixir-ls/issues/530
• https://github.com/elixir-lsp/elixir-ls/issues/449
• https://elixirforum.com/t/dialyzer-in-elixirls-cannot-access-beam-files-for-core-erlang-code/38038

One time this can happen is when using asdf with a "ref" version (e.g. ref:v1.11.4).

There appears to currently be several problems:

• [ ] Error: "Could not get Core Erlang code for: /<dir>/lib/mix/tmp/<file>"
  • There might be nothing that ElixirLS can do in this case, but perhaps the tmp files could be detected and ignored somehow
• [ ] ElixirLS keeps trying to rebuild the dialyzer PLT instead of marking the build as failed and stopping
• [ ] This error should be shown to the user (probably after trying to build a few times)