Move lsp config to local file structure

.config/nvim/lsp/elixirls.lua

@@ -0,0 +1,47 @@
+---@brief
+---
+--- https://github.com/elixir-lsp/elixir-ls
+---
+--- `elixir-ls` can be installed by following the instructions [here](https://github.com/elixir-lsp/elixir-ls#building-and-running).
+---
+--- 1. Download the zip from https://github.com/elixir-lsp/elixir-ls/releases/latest/
+--- 2. Unzip it and make it executable.
+---    ```bash
+---    unzip elixir-ls.zip -d /path/to/elixir-ls
+---    # Unix
+---    chmod +x /path/to/elixir-ls/language_server.sh
+---    ```
+---
+--- **By default, elixir-ls doesn't have a `cmd` set.** This is because nvim-lspconfig does not make assumptions about
+--- your path. You must add the following to your init.vim or init.lua to set `cmd` to the absolute path ($HOME and
+--- ~ are not expanded) of your unzipped elixir-ls.
+---
+--- ```lua
+--- vim.lsp.config('elixirls', {
+---     -- Unix
+---     cmd = { "/path/to/elixir-ls/language_server.sh" };
+---     -- Windows
+---     cmd = { "/path/to/elixir-ls/language_server.bat" };
+---     ...
+--- })
+--- ```
+---
+--- 'root_dir' is chosen like this: if two or more directories containing `mix.exs` were found when searching
+--- directories upward, the second one (higher up) is chosen, with the assumption that it is the root of an umbrella
+--- app. Otherwise the directory containing the single mix.exs that was found is chosen.
+
+---@type vim.lsp.Config
+return {
+  cmd = { 'elixir-ls' },
+  filetypes = { 'elixir', 'eelixir', 'heex', 'surface' },
+  root_dir = function(bufnr, on_dir)
+    local fname = vim.api.nvim_buf_get_name(bufnr)
+    --- Elixir workspaces may have multiple `mix.exs` files, for an "umbrella" layout or monorepo.
+    --- So we specify `limit=2` and treat the highest one (if any) as the root of an umbrella app.
+    local matches = vim.fs.find({ 'mix.exs' }, { upward = true, limit = 2, path = fname })
+    local child_or_root_path, maybe_umbrella_path = unpack(matches)
+    local root_dir = vim.fs.dirname(maybe_umbrella_path or child_or_root_path)
+
+    on_dir(root_dir)
+  end,
+}