This adds generic configuration dictionary support to the elixir-ls
linter. This is useful for disabling its built-in Dialyzer support, for
example, which can improve startup time.
The configuration dictionary is a little verbose. I considered reducing
the user configuration to only the nested settings dictionary (and
having the linter implementation wrap it in the top-level `elixirLS`
dictionary), but leaving it fully configurable simplifies the code and
removes any assumptions about current or future ElixirLS behavior.
4bee0f1743